
Hi Martin, my boy has these reactions to injections all the time, he recently went into the vets for a biopsy, when we picked him up the next day he had the startings of 3 lumps on his neck, by the next day all three were huge, he resembled a dinosaur, bless him, but it is now 3 weeks since his biopsy and they have all gone down now. The first time it happened at the beginning of the year, I was a bit like you, it had been 3 or 4 weeks or so since he had last had an injection, and this was what the vet told me, that it was a reaction to injections he had been having and I was a bit sceptical, she also drained his lump which was right in between in shoulder blades and injected it with an antibiotic, and that lump seemed to get bigger before it went away, but we are used to it now, but I still mention it to the vet, just to make her aware and to make sure nothing gets missed or that anybody gets complacent about it.
Jane