M.R.
15 years??? Wow, you are patient...
So, I highly recommend you religiously soak with a combination of Epsom Salt, Baking Soda, White Vinegar and several drops of essential oils added to your bath. Also, taking an analgesic for a few days will reduce the swelling (Motrin/Advil/Aleve).
But I'm shocked your doc did not do more right at the appointment considering how quickly the cyst grew in size and became painful. Pain is not good. Pain indicates there is a sever blockage and possibly an infection. And if that's the case you need antibiotics to clear this up.
Watch this carefully and if the pain does not subside within a couple of days and the sitz baths don't improve things you need to have it definitively dealt with.
My sister had one of these cysts and she opted for the cut and drain procedure. It was awkward but it worked.