Hi I am 27 yrs if age, after having sex with my boyfriend I a day after I developed a very painful bump between my vagina and the anus, I am a bit worried what could this mean?? the bump is ls not so visible it just looks pinkish reddidh in color, but it is very painful, what can be the reason for this

The immediate reason that pops into my head is an STD.
Unless that is out of the question, get yourself tested, and you boyfriend should do the same.