Huge red hard lump on bum.... boil?

[MedusaIsHavingABadHairDay]

Sorry for the description!
DS2 came to show my his bottom yesterday. He has what looks like it should be a large spot on it.. only there is no head, just a large (really large..twi inches across) red inflamed area which is quite hard and warm to the touch. It hurts to sit.
Getting a docs appointment in our surgery is like finding the Holy Grail, especially after easter! DO you think seeing the nurse would help? IS he likely to need antibiotics or can we just sit him in a hot bath to draw it?

He's 15 and does get spots but nothing like this monster. He has autism and LDs so luckily doesn't mind showing his bum to people as much as most 15 yr olds would!

I wonder if it might be the early stages of a pilonidal sinus? (infected hair follicle, often at the base of the spine). I had one many years ago and I'm afraid to say it was THE most excruciating thing ever. When I say 'early' stages, I mean that it hasn't yet come to a head. If so, you must get him to a doctor (or anyone who can prescribe antibiotics) asap, as if they can't shift it, then it might have to be surgically drained (the aftermath of which is pretty unpleasant).

I really hope I'm wrong though.

I would definitely see a GP as he may need antibiotics.