Am i sick or just growing?!

Im an 18 year old male and turn 19 in july. This time last year i was pretty close to 200 pounds. i now weigh 156-159. I have not grown but maybe an inch or 2 since then and did not start to lose weight until around september 2010. I have not changed my life style in any way as far as dieting or exercise even. I dont sit around much but i am not too athletic either. so the weightloss was kind of random. In the past few months since early january, i have had really strange bowel movements. Going 3 to 4 days without going and then having a week of diarhhea. I became concerned the other day when i noticed blood on the tp. That same day i coughed up a little blood in my saliva. The past few days ive had terrible pains in my neck and i dont know if its all connected or thats just from sleeping on it wrong. I also struggle with chronic back pain and i dont know if its from the weightloss, bad posture, something worse, or all of those together. i have had a difficult time sleeping lately and getting descent nights sleep. Even after taking two xanax i tossed and turned all night long. I am a frequent user of marijuana and smoke just about daily. I do not drink nor do i smoke cigarettes. IF ANYONE can help me with whats going on please tell me.