iphone 4s main camera rarely works, help?

sometimes my main camera will work, but then it will go black and not work for weeks. but when it does work, it will for a month or so, then just stop suddenly, very annoying. its happened since i got it, i just got over it. is there anything i can do to help it? sometimes it will help restarting it, but most of the time it wont. when the camera is about to crash, the screen will turn half black and purple. i just want my camera to work all the time.