Flank Pain? Ulcer? Kidney Problem?

Left flank area hurts and the pain sometimes spreads to my left side. It started about 2 months ago and it will happen a few times in a week, then go away for a week. It usually felt better to sleep or take a painkiller but today it won't and i want to find out what it is. Sometimes it really hurts and sometimes the pain just lingers, but gets worse later in the day.