Please help! I have a very embarring problem (Farting)?

Everyday, when I get home, the first thing I would do is run straight to the bathroom and release the gas. It's really LOUD and sometimes, I fart out slimy poop (almost like diarrhea but thicker..and it stinks too!). I don't know what to do to stop this! I want to join cross country this year but I can't because I'm afraid I will cut the cheese when I run! This farting starts at around 10:00 A.M and every 10 minutes, I would need to fart. I hold it in until I get home. This problem keeps me from staying after school for sport programs! Please help!