Please help. What could this be?!

Please help. What could this be?

So this all started nearly 2 months ago. I originally got sick with a sinus infection and was put on 2 diff antibiotics to clear it up. Between the antibiotics I developed this funny discomfort on my left side by my belly button. Ended up getting really painful where I thought my entire side was going to explode. I was also having occasional diarreaha and loose bm with nausea and loss of appetite I lost about 17lbs. The doctor thought that it might be c difficle or a parasite so they put me on flagyl for 10 days. symptoms slightly improved on the 8th day. Now its weeks later and I am still having pain/discomfort on my left side near my belly button. Sometimes worse than others but its always there although not nearly as bad as originally. Appetite is back but nauseau still occurs off and on. So far I have had blood work, x-ray, catscan, and stool testing. All tests have come back normal. Could it be gallstones. I am having a colonoscopy in a few weeks. I am only in my early 20's.

I can't think of any reason other than irritable bowel or Chrons disease. the pain from an inflamed gall bladder would not be on the left, with that the pain is on the right side just under the ribs. The pain for gall bladder problems can be very very severe too.