I get these too. I have a huge "double" one (it's kinda long, like two saddle sores merged together) on the left, and a leftover small one on the right from last year. They take a LONG time to go away on me, if they ever do. I had a really bad one several years ago on the left, and it finally went away, but it took most of the winter off the bike to get rid of it! Hopefully yours will not be that long-lived.
[Warning: grossness ahead!]
If saddle sores like this do come to a head like your one did and you can lance them yourself (I use a sterilized needle) and get out yellow goop, then keep antibiotic ointment on them, they will usually heal, but mine often won't ever come to a head; they're just way down under the skin and are inflamed and sore but purple in color, not white, so there's no pus near the surface of the skin. And every time I ride, the saddle presses on them, and they're very uncomfortable, to be sure.
I had my doctor take a look at my bad "double" one a few weeks ago when I went for my yearly appointment. She said it was a sebaceous cyst and would have to be removed by a dermatologist. She didn't think it would go away on its own. So, if it's still around come January, I'll get it excised; I'm not willing to deal with this again next year. She said that healing time from the incision would be 2-3 weeks off the bike. I only ride on the trainer in the winter unless we have some really warm days, so I'll just have to plan on a break around that time.
Good luck - saddle sores are no fun at all!
Emily
Emily
2011 Jamis Dakar XC "Toto" - Selle Italia Ldy Gel Flow
2007 Trek Pilot 5.0 WSD "Gloria" - Selle Italia Diva Gel Flow
2004 Bike Friday Petite Pocket Crusoe - Selle Italia Diva Gel Flow