bowel issues for 3 years, age 20. colon cancer?

For the past three years I've had lower right side abdominal pains that came and went. Now I have the pain all the way into my chest on the right, but it isnt crippling pain. I have alternating loose watery stools, constipation, sometimes darker, sometimes lighter, never perfect bowel movements. Its rare I get a good one. I usually feel relieved after a bm but sometimes I get a fullness feeling. I'm only twenty, female. I'm scared its cancer, even though i don't think my family has a history of colon cancer. I also have some nerve pains in the right side of my butt and down my right leg. Sometimes the weird abdominal pain is around in my bellybutton drifting in the right and also left sides. I get nauseous from time to time. pain under right rib/chest. I've got thyroid problems, and a cyst thing with my ovaries. I know I have hemorrhoids. no visible blood in stool, but a lot of undigested food particles. I'm supposed to see a gastro doc soon, but I feel so anxious and scared I'm going nuts. i even went to the er once and the doc there suggested ibs, crohn's, or even UC. Just curious if anyone else has felt these things and has been diagnosed with something?