Poor Skittles - he needs to see a vet asap - this could be pyoderma right now (staph) but can get much worse if he is breaking skin. It could also be other things, but since there are bumps, and it's red - it's likely bacterial, fungal, or parasitic - so you really must get him seen by a vet bc it needs to be treated.
While allergies could be part of the cause, infection could be part of the consequence.
As far as mats - sigh - I hear you on that....you might want to look in the Grooming section for tips.
