8 wk old jack russel wont sleep at night

Question
hi me and my brother have got a 8 wk old jack russell we are having a few problems as he has alot of accidents in the house and barely sleeps at night and seems to be slightly over weight i don't know if this is normal or not as its our 1st pet!at the moment its sleeping in my room i find it really hard to sleep as i can hear it crying and scratching on my bed because it wants to be with me!we were supposed to keep it in the shed at night but when i close the shed door it kept crying and i coudn't stand it, im really worried i might be doing somthing wrong as i was told to only feed it twice a day but it always seems to be hungry!

Answer
First of all Michela, why are you calling the puppy an 'IT' ???
At 8 weeks old he sounds perfectly normal. He is a TINY BABY.
He does not know how to pee outside unless you train him.
It's your job to take the puppy out at least every 2 hours AROUND THE CLOCK to teach him to go outside. Give HIM lots of praise and love when he pees or poops outside, and even a little treat to reinforce the fact that its a good thing to go outside.
In the middle of the night you take him out but don't socialize with him. Just take him out, let him pee and put his right back in the crate. Let him know that night time isn't for playing or socializing.

Secondly, dogs are PACK animals. They don't like to alone and should never be locked out in a shed.  HE doesn't have his litter mates or mother anymore... YOU are his pack.  Let him sleep in your room in a crate so he can see and smell you nearby. As he gets older and learns to pee/poop outside, he will sleep through the night, but it's going to take at least 2 months to teach him.
NEVER EVER punish him when he makes a mistake and goes in the house.
Instead try to catch him in the act and get him quickly outside.
After he's made a mistake it's too late to correct him.... he won't know what your angry at. Never put his nose in pee or poop.
Make a big deal about it when he does go pee/poop outside, praise him and pet him "good boy"!  Positive reinforcement works much better than punishment ever did.
Be patient and be kind, he is so very young and you are responsible for training him to be a good dog and pet. The effort you put into his training and love will directly affect the quality of pet you have when he is older.

You should be feeding him twice a day, once in the morning and once at dinner time. Give him a half a cup each time, and increase it as he gets bigger and older. NO soft food, it's not good for them, bad for their teeth and makes them have diarrhea. Feed only crunchy food, and keep fresh water down for him until 6:00pm to cut down on the peeing at night. If he is insatiable and looks overweight, you must have him checked for worms. The puppy should have already had at least one deworming from the breeder and he needs another one at 8 weeks. He should already have had his first set of vaccinations by this age too, and if he hasn't, it's important to get him to a veterinarian ASAP. Usually a distended belly in an indication of worms and you need to get rid of them right away.
I'll be happy to help you anytime with any question.
You've taken on a huge responsibility getting a new puppy, so lets make sure you do it right!
Write to me anytime, and be patient and loving to your new pup.
Best of luck.