Why can't my digestion get back to normal?

For the past 6-7 days I have felt the constant urge to either pass gas or just go and drop weight in the toilet. I have slight bloating in my lower abdomen which also likes to make a lot of gurgling noises often as well. About a week ago I was prescribed Biaxin XL which i took 2x a day for 3 days. Well on Friday night 11/19/10, I felt like I was getting a bit of normal gas. However I found that it was not normal once the pressure of it was still there the next morning. I went to the doc last monday and he said that biaxin can do some good damage to your stomach and told me i was a bit backed up; then he told me to try some milk of magnesia. Well I did that night and went really well but still no relief. So after a fairly uncomfortable Thanksgiving week I can now go to the bathroom a bit but my stools are about the size of a finger and don't like to come out without me making myself sit on the pot which I am now doing at least 5 times a day now. I can also only seem to get out a few of these at a time. Could these abnormal sizes due to my colon being swollen and overworked? My normal BMs were usually getting out 2-3 good sized sausages and feeling completely relieved for the day, having 1 BM a day. I usually have a cast iron stomach and don't suffer from these kinds of things.I've been feeling so filled up lately i sometimes don't even want to eat much. I've been on a pretty good fiber diet, about 1-2 fruits a day veggies and trying not to eat too much junk food, which is a diet I am seriously tired of. I've even stopped drinking my 2 cups of tea with milk a day because of the dairy products. Even stopping my one a day vitamns because of the calcium in them which have been keeping me from getting sick . I've been drinking plenty of water as well, and also eating 2 cups of Activia a day, but i'm scared that I might be stuck like this for a while. My parents don't seem too concerned which doesn't offer much reassurance on my part because they say at least I'm going. I am going back to the doc on Monday for maybe another x-ray and further discussion if this doesn't clear up. I'm a 19yr old male by the way, and would just like to get back to my healthy pooping self lol.