Very frustrating, reoccuring digestive problem

I am a 23 year old male.  Recently, about two or so months ago, I started to notice a change in my eating habits (no appetite) and changes in bowel movements.  The lack of appetite is sometimes accompanied by nausea, although I have been associating that with my decreased intake of food.  Anyway, I starting noticing a lot of mucus in my stool, sometimes a bowel movement would consist mostly of mucus.  The mucus in stool has been partnered with the frequent urge to go to the bathroom and release my bowels, however, there is usually nothing there except gas and mucus and some stool.  Even more recently, I began to notice a sharp pain in my lower back, near my spine, on the right side.  This pain is really only noticeable when I'm sitting or have been sitting for too long.  Finally having enough, I went to a doctor, who decided it must be Colitis (inflammation of the bowels) and prescribed a short regiment of pills.  Because this did not help anything and with the addition of the pain to my back, I went to see a specialist.  He told me to stop the pills, put me on a high fiber diet, and said to give it two weeks.  After no improvement, he scheduled an x-ray of my lower back and a colonoscopy, thinking it could be an internal hemorrhoid or something of the like.  Well, the x-ray and colonoscopy came back clean, minus a very slight anal fissure.  He prescribed me some hydrocortisone gel to apply twice daily, and that was it.  Well, after doing so for about two weeks, the problem persists.  Now, I am very confused (and lacking in my bank account, I might add) but still have no real clue what is going on.  I feel that anything serious (like cancer,etc) would have shown up on the x-ray or would have been spotted in the colonoscopy...I would love to hear some thoughts on the matter before I go see yet ANOTHER doctor and spend my hard-earned money on procedures/medications that are doing nothing to help me.  Any suggestions are greatly appreciated!