Hi there - sorry to hear about your problem. Last year my husband had the same thing from how you describe it. At the time we weren't sure how to handle it as we were new in the area and not signed on to a doctor (also he refuses to see doctors unless he's so sick I have to drag him there myself). So, we treated it two ways - firstly, hot baths with tea tree oil in the water (he also applied the oil directly to the lump as this tended to act as an antiseptic/anelgesic and stop the pain); lots of reiki from me. Within a couple of days the lump burst to his great relief, but we kept up the regime for another two days to check that no infection set in. It's not come back.
Afterwards he spoke to his mum and she said that there was a very common condition called "lorry driver's bum" !! which basically affected people who sit a lot ie office workers,delivery drivers etc. And that it's important to get it checked out with a Doc as it can get nasty and needs antibiotics or even an op to remove if it doesn't respond. She said my hubby was very lucky!
We think it was a stress related issue, also related to my hubby giving up smoking (all the poisons running out of his body and collecting in that area); I also have a theory about lower chakra blockages but for him this is a step too far! But in terms of a recurrence it would probably be a good idea (if you are into it) to check out the functions of the lower chakras (especially the base) just to see anything rings a bell.
Hope you get it sorted, take care, Sue.
PS Unless you've used teatree oil before I'd go easy and not apply directly to the skin cos it can be very drying - unless you have access to a handy aromatherapist who can help you out. A few drops in a hot bath on on a hot flannel etc would probably help ease the pain in the short term though.