Whats using up my samsung?

[I hearts you]

Ok I have a samsung galaxy ace and lately ive been charging it and than it just dies quicker, heres some imformation I can give:
-i used to.charge it just before I went to bed, than during school it would last the whole day, I used instagram and messaging and a few.google searches
-i moved away and dont go to school yet so I have just been on my ipod and phone all day,
- I use viber most of the day coz I talk to my friend
- I.use instagram only rarely now coz I can use it.on my ipod
-i am now in nothern territory so I use it alot and charge.it alot coz it keeps getting low
- ive turned all my brightness down etc
- I charge it at night now and when I wake up it says charge battery 0.o
-i sometimes have to take it out its charge because we are going somewhere and I dont wanna overheat it but its does get hot while charging :/

And for the credit/data:
I.hve 500mb and I use It up really quickly lately eversince I got viber.it seems to go quick
Is viber causing it?
It says that I watch you tube which I dont
And I always close my apps


Ive had it for about half a year, ill.buy a new one when I have a job
Thanks please help x

[delta]

I own an Ace as well
The battery life drops after a 500 charges and then keeps dropping further after that
This is true for any phone
Any of the following could solve your problem:
If you started charging your phone with the USB cable instead of the AC adapted, that could be a problem
Try taking a backup of all your data, and then do a factory reset
Try keeping the 3g/data off for a while and then use and see how the battery holds up
Try draining the battery completely, till the phone turns off on its own, and then charge it overnight, it wont overheat and melt, i do that when i have to calibrate battery