Left side pain?

[the_soap_guy]

Hello, I am 23 and am concerned about some recent things I did leading to possible health problems.  First of all, I'm kind of new to the whole anal sex thing and recently did it a few times over the past couple weeks.  I was the bottom and it was painful for a little bit but then it got better after a few seconds.  When I get home, though, I feel queasy so I go into the bathroom and end up shitting out a little bit of blood like diarrhea.  Not a lot, but the only thing that was in the toilet was like a teaspoon of blood.  A week or so later, I do it again and don't shit out any blood... and, uh, sorry if this post is kind of graphic by the way... but I notice that there's some blood in parts of my shit.  Now I don't really think anything of it because I feel like a lot of people bleed when they do it... but then again I'm not totally sure?

But now I have this strange pain in the left side of my stomach under my ribs.  It doesn't hurt that much, but when I take a deep breath, I feel something hurt for a few seconds and I'm kind of freaking out.  I Googled what this could be and am thinking I might have ulcerative colitis?  Am I jumping the gun or should I get this checked out at the doctor's immediately?

Thanks for the help...