
From the brief description, it sounds very similar to something my Stafford bitch had years ago too.
We never did find out what she had come into contact with, but it was definitely out on a walk, so assume either nettle stings or some type of insect bite.
I too would recommend an anti-histamine (IF the lumps/bumps are some sort of bite/sting/allergic reaction), though I would only recommend giving
half a tablet. Plenty for a Stafford b*tch.
Try it for a couple of days max. and if that hasn't worked, then a trip to the vet is probably my best advice.