Alternating Diarrhea/constipation, Bloating, Gas, What the Heck?

I have no idea what's wrong with me, and apparently neither does anyone else. Also, this is exceedingly gross. You have been warned.

Tuesday night I ended up having to go to the bathroom with diarrhea three times before nine a.m. I thought maybe it was the turkey sandwich I'd eaten a couple hours before bed, or maybe even the Wendy's I had for lunch that day. Wednesday I felt a little rough, but by that night I was completely miserable. The diarrhea had given way to constipation, so that no matter how hard I tried nothing happened -- and if it did, it was watery and runny like diarrhea, but it always felt like there was a lot more that just wasn't coming out. I also panicked a little bit because I noticed a small amount of blood on the toilet paper. That night, it also became extremely painful (and pretty much impossible) to pass stool. It's like a strange burning, sore sensation that only happens when I'm straining.

Thursday I left class early and went to my university's health center, where the doctor gave me Dicyclomine to take three times daily for the horrendous lower abdominal cramps I was experiencing. It helps the cramps for about twenty minutes after I take a pill, but then it just comes right back.

Yesterday I actually felt relatively decent, so I thought hopefully I'd just caught a strange bug and it had passed. Just before bed I had to use the bathroom, and after straining and fighting through the terrible burning pain in the anus, something finally gave and I felt a tremendous relief. So yay, I actually got to sleep easily for the first time in days. Then I woke up this morning and I'm back to square one. The cramping isn't quite as bad, but now I've got two additional problems: bloating and gas. The constipation is still there, as well as the odd bouts of diarrhea when something finally *does* happen. I asked a pharmacist at Rite Aid and he suggested antacids and Gas-X. It's helped the bloating and uncomfortable full feeling I woke up with this morning, but the constipation isn't going anywhere.

What in the world is wrong with me? I have a bad habit of trying to diagnose myself on the internet, so naturally with these symptoms I'm victim of about sixty different diseases, including a couple interesting varieties of cancer. Thing is, I'm 22 so I doubt it's anything too serious, but it's bothersome and painful nonetheless. Not to mention I haven't had a good night's sleep in almost a week. This is the first time I've ever been constipated in my life, or had anything remotely resembling this set of symptoms, so I'm not only miserable but somewhat disturbed as well. Any ideas what's going on?