Why won't my iPhone charge?

I have an iPhone 4 (32 GB) and I got it in september this year. I never dropped it on the ground, floor, water, etc. I've been really careful with it. Two days ago my phone only had 10% and I tried to charge it. And it didn't charged? I was really confused, that never happend to me before. I took the charge out and plug it in again, but still didn't work. Then I tried going on the internet and see what other people do to fix it. I've tried so many things, but nothing worked. I tried again today and it finally worked, I left to charge it for about an hour and I only see that it have 3% ! And now it doesn't says that it charge. I don't really know what to do. Help?