I have a single semi-hard red bump about the size of a large pimple located on the outer right lip of my vagina. I'm actually not even sure if it would be considered the "lip" at this point, as it is rather close to where the genital area meets the upper, inner leg. I noticed it first while shaving. I haven't shaved since I noticed it (since Thursday) and the size seemed to subside a little bit. It is slightly tender/itchy but only when touched, like a pimple would be. I actually had my annual obgyn exam today and my OB/GYN doctor merely asked if I had cut myself shaving, I told him no, and that was the extent of the discussion about the bump. I just recently popped it (probably not the best idea), and a little bit of yellowish puss came out followed by a little blood. Is it possible this is just a pimple or something to be concerned about?

It could be a pimple, it could be an ingrown hair (especially because you shave), it could be an STD, etc. etc.

There's really no way to tell you which one it is. I'd go back to your doctor and ask him what it is, and if you should be concerned. If it's an ingrown hair he'll have to remove it for you.