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.
Bumps can be many things often not STD related. Best advice is to see a Dr for proper diagnosis.