I think you should see a kineasyologist. It sounds like you could have candida, and they will be able to pick this up, and treat you. GP's wont be able to test for this. The kineasyologist will muscle test your body to pick up if your deficient in anything, and if you are having a reaction to any foods or anything else your coming into contact with. Basically, your body tells them what is going on with it. Candida is very common, especially if you have ever taken antibiotics for anything. The problem is it is a very nasty condition to have, and very common to have. Symptoms are not just thrush! In fact you can have it and not have thrush. Depression, irritability, foggy head, headaches, concentration problems, PMT/S, etc etc etc. What happens in candida is that your body is producing too much Oestrogen that your liver cannot process. Another symptom is mucas on the stools, and anus discharge could therefore be connected this.
Also, try dabbing TCP (diluted) on your anus. Any infection, can produce puss and smell, and could be helped by this.
Alternatively, sexually transmitted disease tests should rule that side of things out!
I've had simalar problems I'm 20 and about a year ago. I noticed when I had a bowel movement that I would wipe and it would be like a whole bunch of clear slimy stuff. Nothing has changed I haven't been cheaked out. I also have hemmoriods also but only bad when I consitpated. It seems like that it's always a small piece hanging out my rectum no mater what.