Sounds like there may be a task left open in the background. Press and hold the back arrow to see if there are any tasks left open? If not try a soft reset first by pressing and holding the vol down+power button. You shouldn't lose any data doing this but some have reported their clock resetting.
Another thing to check. Goto settigs>Applications>photos+camera. Is Auto upload to Skydrive on or off? If it is on, your phone may have apent hours trying to upload to Skydrive if you have a slow internet connection. If connection is slow, you might want to consider turning this off.
If all else you may need to replace the battery.