My dog has allergies...?

So here's my situation. My dog has had this issue for as long as I can remember. He always licks his paws and bites at them. Not the pad part but in between. He does this and they end up getting really red and sore and sometimes even end up bleeding. He ends up growling at myself and anyone else in my family if we even try to get a look at them. I'm uming he does this because something is irritating his skin such as allergies. We've tried everything. We've taken him to the vet but they only give us this really expensive medication that doesn't really end up helping. We've tried different kinds of sprays. We give him baths regularly. Nothing helps. Lately it's been where he has also been biting and scratching his tail and torso usually to the point of bleeding. Just last week no one was watching him and he ended up biting his tail through the muscle. Very gory. Please help if you have any suggestions or you have the same problem! Thank you in advanced!