Go see a doctor. It may be cancer.
^^^^Because Google and WebMD don't scare us enough....*eyeroll*
OP, I know you posted this 4 years ago, but I'm going to post here anyways just in case someone else comes across this thread. First and MOST important!!! IT'S PROBABLY NOT CANCER. You've got a better chance of hitting the lottery jackpot than you do that this is cancer. You've mentioned it pops like a zit and leaves a sore, then inevitably fills back up again. You can't really 'pop' a cancer tumor, not like that anyways, so don't let AntiDetergent's comment scare you.
I had the exact same thing (same place too). On the surface, it appeared to be the size of a medium grape, and it was rock hard. It was not that large when I first noticed it 10 years ago. Goodness knows I tried over the years to drain it, pop it, whatever, and no luck. My gyn refused to do anything about it because "It's a perianal cyst, which is a GI issue. I'm not touching it." My GI doctor said "It's close to the opening of your vagina, making it a reproductive issue. I'm not touching it."
Friday night, it started hurting, and grew bigger rather rapidly. I told my husband I was going to call my gyn on Monday and beg for something to be done, because I'd had enough of the blasted thing.
Last night (Sunday night), I went to the bathroom and noticed a purulent pink fluid on the toilet paper, and sure enough, the 'new' infection was draining. I did the hot compresses (things you'd do for a typical abscess/boil/etc), and when I started squeezing, I got all the 'new' stuff successfully out, and hard stuff started coming out. After a few hours of alternating hot compresses and drainage measures, I got the last of the crap that had been there for a decade. And then I promptly vomited, because it was gross. It left a small hole in my skin, which should not be surprising if this has happened to you...pores are very small and you pretty much just forced a marble out through it. It's going to leave a hole.
I had one doctor tell me it was a Bartholin cyst, another tell me it was a sebaceous cyst, another told me it was an ingrown hair, and until it started actually bothering me about 4 months ago (not painful, just a nuisance, because it was right near the vaginal opening), all of them said there was no need to remove it.
What is probably happening is that the pore (the hole) is not large enough to allow the pocket (what was formerly filled with hardened stuff and pus) to drain freely.
Long story short? YES, call your doctor. You may need to have a procedure done that will allow the pocket to drain freely, but NO, it is MOST LIKELY NOT CANCER.
I hope this helps anyone who might come across this thread.