Rash on dogs belly

My 16 month old male Hungarian vizsla seems to be prone to hives on his underside, he has so little fur there I suppose no protection. The other day he rolled in a long dead rabbit carcass, which was nice . The next day his belly and in the creases of his legs ( I want to say armpits but as dogs have no arms?! Leg pits?) were covered in spots with white heads. They didn't seem to bother him and as they popped they dried over. Is this likely to have been bacterial rather than allergic? I had read that the piriton in the pks of 30 are suitable for dogs so have bought some today for the next time he get the hives and some tea tree cream incase of spots. Is this suitable? I am also unsure of how many tabs to give him. He weighs 23.6 kilos.

Thank you

Jade

Have the spots dried out leaving like a small flaky white skin patches?

No they just dried out to a small scab which quickly fell off. They didn't seem to itch him as he paid them no attention.

If you give your vet a phone they should be able to work out an exact dosage over the phone

My vet is a bit of a misery, I think if I rang to ask I would just get told off for self prescribing