IPhone won't let me make app purchases?

I recently got an iPhone 5s, for the first week I was able to make app purchases with no problem. Now whenever I try to purchase anything I get a message stating that my Apple ID couldn't be found or my password is incorrect. I know that my password is correct (I use the finger scanner, then put manually enter in my password when that doesn't work) anyone have any idea on how to fix it?

My suggestion would be to call Apple and ask if your account is locked. Your account could be locked for a number of reasons. Contact them by calling 800-MY-APPLE/800-692-7753 (US/Canada) to ask what may be going wrong.