Did the doctor examine you? Look at this bump?
It could be a genital wart, but those are usually painless and probably wouldn't be causing the sensitivity. It could be molluscum contagiosum, which is another STD. They look similar, but warts look a little more like cauliflower and MC looks sort of like a pencil eraser (vaguely). There is sometimes a dimple in the middle of it. Your doctor should take a look to determine this for sure.
The incubation period (time from infection to symptoms) for HPV can be a few weeks to several months. The incubation period for MC is a week to 6 months, with an average of 2-3 months.
If it's either of these, it probably didn't come from the encounter with the sex worker, because of the timing and you used a condom. Neither are spread by oral sex commonly.
Let us know what the doctor says, or said if they've already seen it.