I could fill this line with the problems I have had and am having!

Question
Hi Joe,
Hopefully you can help me with the problems that I am having since no one in PA seems to know a thing about fish and tanks except how much money is going into their register!
I am VERY new to owning fish or I guess I should say, killing fish and I'm getting upset cause I know it's something I'm doing or NOT doing that caused 3 of them to die yesterday as well as 2 others last week.  I have a 10 gallon tank, well water, 1 mickey mouse platy, 8 tetras and about 20 fry, or as I call them, baby mickey mouse platys.
I was told from the guy at the pet store to buy 4 tetras to start the tank, let it cycle for 4-10 days and when the water cleared I could add more fish, up to 10 total for the tank size. I have now found that I should have waited about 4 weeks for the tank to cycle but that's a little too late! The fry were born in the plastic bag on the way home from the pet store so I went back and was told to buy the breeding box that attaches to the side of the tank, so that is where they currently are however, I would like to and know I have to get another tank or a much larger tank before they get larger.
I don't know if you need anymore info, if you do, just ask... as I said I am new to this, I have had the tank 2 weeks. Now onto the problems...
I came home from camping last weekend to a dead fish, I pulled him out and watched the others for a few minutes and all seemed fine.
The 4 tetras we started with show no signs of any sickness, at least not as far as I can see. I also had 3 other tetras one of which I saw swimming at the top yesterday morning so I watched him for a few minutes when he started floating to the bottom, head first in a spiral... I got him out right away and he died within 2 minutes of me pulling him out of the tank. I started watching the others and as I know that disease spreads when I noticed one of my Mickey Mouse Platys had white lips that looked "fuzzy" and he was just sitting at the bottom of the tank, I pulled him out and within an hour he was dead. I also noticed another MM platy had very scraggly fins, I thought fin rot but he also had red spots by his tail that were not there before so I decided to go back to the pet store with one dead fish and one sick one. The boy at the store said I probably have a parasite. When I asked him what I can do he really offered me nothing more than, "Clean the tank" He said it's because my Nitrite levels are off the charts.
Now, I have vacuumed the gravel, SEVERAL times, changed the water about 4 or 5 times and when changing the water it has been abut a 50% change each time because I can't get the nitrite levels down! I bought a gel like additive for the tank - ammonia detox by Tetra Aqua- and it does not seem to be working yet however it has only been about 14 hours since adding. It said on the bottle I could double the does so I added another half dose cause I am afraid of hurting the fish.  
BEFORE adding the detox we did buy Fungus Cure and Super Ick Cure by Aquarium Pharmaceuticals Inc, we added 2 capsules of both as directed on the package. When I was at the store I advised the boy what we were using and he said, don't use it, use Quick Cure, so we bought that, went home, changed the water 50% AGAIN and we put only 3 drops in instead of the 5 as directed as we are afraid of over medicating them.
Can you lead me in the right direction here before I pull my hair out!!! I hate to hurt any animal and I know I am causing these poor guys so much stress and sickness!  As of today I see 2 small tetras that look like they have white fungus on the tips of their fins, I have added the ammonia detox (last evening) and about 30 minutes after adding that the fish became very active, the oldest 4 tetras are swimming around like lunatics, just back and fourth all day, my boyfriend said they are trying to get the heck out of there, I hope they are just playing! I'm trying to wait for the capsules I added to cycle through before I add more of the Quick Cure, I assume that is 48 hours as the package directs me to add more capsules every 48 hours. The biggest problem I am having is getting my Nitrite level to drop... they are at a toxic level.. between 5.0 and 10.0 and I cannot get them down, as I have said, I have changed the water (many times), vacuumed the gravel,  added the detox and even removed most of the gravel to get rid of any "mess" that may have been hiding. I had rocks in the tank that had come from a creek in our yard I also removed them about an hour ago cause only God knows what they are holding. I also tested my well water and everything seems fine except the hardness, could this be contributing???  I just don't want to hurt anymore of my fish!
Sorry so long and random!
Thank you for your time!
Dawn

Answer
Dawn,
The first thing you need to do is relax.
Your question is quite long and I will do my best to get you set up.
A 10 gallon tank is small for all those fry anyway.
If they survive, they will need 20 or more gallons.
The rule is an inch of fish per gallon.

I have well water also and hardness is nothing to be concerned about.

What you need to do is buy a product called Bio Spira if you can find it.

You can add fish and Bio Spira at the same time and your tank will cycle within 3 days and no fish will die.

Bio Spira is the bacteria aquariums need to keep fish living.

You will see the nitrites and nitrates even out and all will be fine.

All those fish that died were killed by ammonia poisoning.
The pet shops are a disgrace telling people to cycle their tanks with fish and no Bio Spira.

Ammonia to a fishes gills is like carbon monoxide to our lungs.
Let me know if you find Bio Spira and also, don't clean your tank more than once every month or so.

Too much is not good.