Small bump after rough sex

I wouldn't assume it is an std, for one they usually don't work that fast.  It sounds like you have some torn skin.  Some women have a frequent problem with that, especially during rough sex.  A few unfortunate women get tears really easy for almost nothing.  It can also happen if you scrub your grown too aggressively, this happened to my wife.  I think we learned about this on this very site, SteadyHealth.

There really could be some liquid forming in it.  The body tries to protect itself by form a soft barrier to protect the irritated area.  Blisters are a good example of this.  My main concern at this point would be getting an infection.

Do not scratch if starts to itch!  This will often keep reopening the injury, leading to more pain and more itching.  It becomes a never ending cycle that won't heal.  The nurse I spoke to suggested using lotions used for diaper rash, such as A&D ointment and desitin.  She also suggested Vaseline if we didn't have anything else, but bag balm would work and Eucirin would be a good choice.  We went with eucerin. You need the original formula that is very thick and hard to spread.  Apply it to the injury to protect it and to keep air off of it (which causes it to itch).  Reapply as needed.  It worked very well and it healed rapidly after that.  It was kinda messy, though, and it took a bit to adjust to having a cream down there all the time for a few days.

Keep an eye on it and go see the doctor if it looks infected.  An infection there can be really bad, especially if it gets strep which can eat flesh.  (Got some in my knee a while back and it nearly killed me.)  Take it easy during sex until it heals or even abstain for a few days.

I am not a doctor and it might not be anything like I suggested.  Getting another opinion would be a good idea.  I really don't think it is an std but keep an eye on it for while just in case.  And please go to the doctor at the first sign of trouble.

Turn about is fair play, and since you were generous enough to do something just to please him and even got hurt by it, I would hope he intends to return the favor.  Tell him he had it his way last time, its your turn now.  Might I suggest a long episode of oral sex (for you, not him), the relaxation would be good for you. Unless he just isn't any good at it in which case he should learn by asking you what works and what doesn't.