My old dog Jamie started licking and biting the top of his front paw. Due to all the hair, it was very difficult to see what it was - there was no obvious lump. I found out what it was when he was sitting on my knee and I just put my hand on his paw - and SPLAT - we both got a bit of a shock to be hit in the face by blood and pus :shock:
It was a very soft infected lump, caused by licking and sweat between the toes. The vet prescribed anitbiotics to clear up the infection and hibiscrub as aftercare. I continued with the hibiscrub for a while and the problem didn't return.
Until you see the vets, cleaning the area with hibiscrub or iodine wash/solution will keep it clean and will help to ease any infection.