Had anal bleeding for a little bit over a month now……?

(I just posted this in mens health, but wanted to see more answers)

For the last month or so when I have been going to the bathroom (#2) I have been seeing blood. Well for the first 2 weeks I was like okay this is weird but nothing to get worked up about, and then I started to have pain in that area throughout the day. Well I started to smoke pot to help ease the pain, but now its gotten really excruciating. And yesterday was the first time I noticed I even had blood in my boxers, so now its not only when I go to the bathroom. I saw some previous questions on this subject and some people mentioned colon cancer and I started freaking the heck out!! I'm 19 if that helps. Well I want to go to the doctor but can someone tell me what there exactly going to do. If there going to be doing something crazy then are there any over the counter drugs that would help. I'm like literally in pain throughout the day. Thanks.
And if anyone has gone to the doctor for this before. How "extensive" was the check up??