What causes cancer is such a complex subject, you couldn't even fathom all the variables. One can't determine what makes some people have cancer, and some don't. You can find similarities, but it's not cut and dry in those instances.

There are people who smokes cigarettes and never get lung cancer. There are people who are healthier than an angel, and they get cancer.

From my experience with Testicular cancer, you'll either feel nothing, or in the later stages feel unbearable pain you would mistaken for another type of pain. It's not like "oh geez, I feel a little pain when I'm doing this, I have cancer." It's more like "Jesus, I am in so much pain, I have trouble getting around." I thought that pain was injuring myself from working out too much, not from cancer.

Your pain I doubt is cancer-related. It's great to be concerned about your health, but you shouldn't get overly paranoid about having cancer.

You should be enjoying life, but if you'd end up one day having cancer, you want to enjoy every minute before you do. You'd know what hell feels like.

In the meantime, as great ol' Granny here suggests, use a vaporizer =)