Bumps can be many things often not STD related. Best advice is to see a Dr for proper diagnosis.
A bump is not indicative of an STD, even if it is red.
Herpes may or may not be red, but it is generally clustered and painful.
A primary syphilis chancre would look like a crater, which would be round in shape and have a hard border.
If it worries you, throw any and all embarrassment to the wind and go see your doctor.