Claire, you have my sympathy - it sounds like it's been a real nightmare for you!
I've had a couple of minor issues with cellulitis - just as a red area on my leg and not really painful, and it's cleared up quickly with antibiotics. If I remember correctly the first and worst time was one December, and well before my T2 diagnosis though.
What I DID have a couple of summers ago that sounds similar and was excruciatingly painful and lasted for months was weeping oedema. I've had oedema , usually as a summer time swollen legs "inconvenience" for many years without any real problems, and which suddenly developed into this terrible blistery weeping version. I discovered afterwards that swollen legs etc, are listed as a known potential serious side effect of amlodipine which I was prescribed as a temporary measure when my normal blood pressure meds weren't available, and I believe in retrospect that this seriously aggravated my previously well controlled and trouble free oedema. It was the only time I've had a problem - and during this summer heat wave I've just had my usual fat puffy legs.