Sounds like Irritatable Bowl Syndrom (IBS), something I have been dealing with since I was about 20 years old. You really should see a doctor, nothing can be diagnosed without seeing one. Are you old enough to drive? If so, call your family doctor, make your own appointment, and drive yourself there. They should have your insurance information of file.
What has helped me is drinking Metamucil twice a day. (I drink a glass around 8am and the second glass around 1pm. If I seem to be having abnormally bad stomach issues I'll drink a third glass later in the day). Since I have been doing this I have rarely had the issues as you have described above.
Good Luck!