dramatic death!

Question
hey Jamie, unfortuantely the aquarium now has a lower population....
About 3 days ago, it started.My last black molly started acting weird.It started to go to the corners and lie down there. Unless the other fish touched it, it wouldn't move, it was alive and moving it's tail. That carried on for about 3 days, i was getting more and more worried everyday, i tried to look it up but nothing helped.

Then yesterday, i came back from shopping and went upstairs to check on the molly. It was fine, but i just kept on looking at it. Then, it went on it's back on the gravel. I could see those big gill things breathing (sorry, i don't know the proper term) It was obviouly dying,i wanted to see what would happen, so i continued to watch. While on it's back the fins were frozen butthe mouth and gills were moving. Eventually the gills stayed open and froze. i wasn'r sure if it was dead or just lying down so i got out the fish net and tapped it very lightly, i knew it was dead when it didn't run away , most fish run away at the sight of the net. So i picked up and flushed it. Now, what i wanted to ask you was, what caused this horrible death. (sorry about the long novel) so please let me know thanks.
*^Monika^*

Answer
You are still going through the cycle, and you will most likely lose even more fish.  You just need to change 50% of the water everytime the ammonia and nitrite levels reach .25 and that's the best you can do.  These things happen when you set up a new aquarium, but after that first 2 months, it gets better.  I am sorry about your fish