What Causes Abdominal Pain,nausea And Frequent Urination?

My periods have been regular since I started in middle school. I've never really had problems besides the occasional cramps and mood swings. This past year I started college and my periods starting coming with more cramping and such but I assumed it was the change affecting it. Two times in the past 4 months I've had periods that are later than normal (beyond 30 days) and have been more painful especially in my lower abdomen into my pelvis. This past month I came home from college for the summer and lost about 6 pounds by dieting. Then I started having really bad abdominal pains on and off that felt like my upper abdomen was burning (I was also taking a colon cleanse for 2 weeks but stopped when these symptoms started). Then I got very bloated so I thought my period was coming soon. Almost 2 weeks later I woke up at night with upper abdominal pains that were excruciating for almost an hour. I went to the doctor and told her about it along with increased belching/feeling the need to belch and mild more constant stomach pains. She thought it might be either gastritis or gallbladder stones (even though I'm 19 and don't eat greasy foods or drink). She gave me medicine for the former to see if that helped and that night I felt almost like I had a fever but I've still been taking the meds. 3 days later (today) I got my period but now the pain in my lower abdomen is excruciating and I feel nauseous on and off and I've tried heating pads, ice, Midol, hot tea, and rest but it won't go away. I've had an increased urge to urinate and extremely frequent bowel movements. What's going on with my body??? Should I be worried?