This sounds like you give yourself an "internal" massage of your prostate gland and/or seminal vesicles. During a rectal exam, providers sometimes intentionally massage these organs and express fluid, i.e. semen or its prostatic components. If you don't have a spontaneous discharge from the penis or discomfort on urination, you can safely assume nothing is wrong and I very much doubt you have an STD. But if if continues frequently when defecating, see a health care provider to be on the safe side.
Good luck-- HHH, MD
yea, but i forgot to mention i recieved unprotected oral sex, but can that cause something? today i also noticed the tip of my penis felt wet even though it was dry.