Got an ulcer on my penis. wth?

Not a good sign: An ulcer there is never a good sign, and could mean you have a very serious venereal disease. You should run, don't walk, to a clinic and be tested. Oh, and please wear a condom! good luck.

See a Doctor: Stop wondering and go see a doctor and get a diagnosis. It could be a pimple, a skin infection or a sexually transmitted disease you will want to get treated.

See a doc ASAP!: If not painful it could be primary syphilis - needs treatment with penicillin immediately. If painful, it could be herpes or lymphogranuloma venereum - these require treatment as well. Until then, it is important that you abstain from sexual activity or else you will spread the diseases. It is also ethically important to tell your sexual partners to be tested for stds, to stop transmission.