I had sex with my girlfriend long after she went dry. the next morning i had a red bump at the base of my penis. is this just from friction?

Probably friction: Minor trauma to genital skin is often the result of enthusiastic unlubricated sexual intercourse. However, because there are plenty of bacteria in your personal Biome (look that up if you like) that can cause infection of traumatized skin, you might consider a OTC antibiotic for a few days. Further problems, consult your practitioner. :)

Possibly: if there is no discharge or pain it should be fine to just monitor