Prednisone is a terrible drug. Just terrible. However, for a week or so and for extreme cases of contact dermatitis ("Poison Ivy"), or other severe allergic reactions, it is wonderful. Yeah, wally world will sell it to you on their super saver prescription plan for four bucks, which is why I suggested, above, that the OP go back to his doctor. But then, suffering myself from Cassandra Syndrome, no one ever listens to me.
Tecnu is good E36 M3. I have a bottle of it next to the sink and a super concentrate formula upstairs. After the rash breaks out, though, it isn't as good. Doesn't hurt, just doesn't help much either. But post exposure, the stuff is magic.
Interesting on the Jewel Weed, FT.