I've heard that Lyme Disease is very hard to get rid of, and that the effects of it can actually last a lifetime. As best I recall, bowel problems are associated with it. :-(
Still, have you checked with your doctor to see if maybe your current problems are linked to linger Lyme Disease and if there's some additional treatments you might try?
While it will certainly make you feel better to get a colonoscopy (which looks for colon cancer), or, at the very least, a blood test, colon cancer is pretty rare in young people--it's a disease that doesn't usually start showing up until middle age and, especially, in the senior years--and is especially rare in young people without a family history of colon cancer (as far as I know, there is no link between a family history of some other kind of cancer and colon cancer, but, like I said, you can always get a colonoscopy to ease your mind, and that will also check for other, lower colon problems).
Stress, especially after having such bad health last year, may be a large part of your problems. It certainly doesn't help existing problems, that's for sure. Have you thought about ways to try and lessen the stress, such meeting with a therapist, a group (I know there are groups out there for people with a family member with cancer--ask at your local hospital or look in your newspaper), or Asian forms of meditation/yoga/tai chi?
Have you seen a doctor about getting prescription anti-spasmodics? They're very much hit-or-miss, so you may have to try several to find one that works for you.