It sounds like bartholins gland cyst. or skenes duct cyst. very normal even though they really suck but if it gets worse sometimes have to be surgerical removed
I've had something similar. Mine turned out to be a ingrown hair that kept getting infected. At first I had no idea what it was until I realized I could see something black when I'd squeeze it, finally I told a needle and got the hair looped around it and pulled, then pulled with tweezers. It ended up being about 2 1/2 inches long. No clue how long it had been growing. lol. Sorry if this is no help, I just figured it could be a possibility for you aswell.