Rash/Bites/Poison Ivy? on Gavin

Need some advice on a skin issue with Gavin. He has had it for about a week and I was thinking it was poison ivy. He is in it all the time on the trails as I was under the mistaken thought that dogs could not get it. It seemed to behave as poison ivy. A small rash that kinda blistered and discharged a small bit of clear liquid, then dried up and scabbed over. It has been itchy too; some licking going on. It is on the tops of 3 out of 4 paws just above the ankle and he also has a spot inside one hip. Some of the scabs have been shed and are caught in the fur. Some spots are only one or two scabs, others have a few more. Treatment so far is cleaning with a disinfecting shampoo from the vet and benedryl. Two benadryl do not seem to touch the itching too much and it makes him super sleepy so I stopped with that. He is also pretty good about stopping when told, but he does sneak off and hide to lick sometimes. Does anyone have any idea what it may be? My pictures not great, but the best I could do. They show the worst spot on his body. Thanks in advance.