My gf is going through this currently. She had a small rash on her leg that spread bad. She got on meds and it went away but its starting to come back in the same spot on her leg so she actually needed to go give a skin sample at the doctors so the can find out what she is allergic to. We originally thought hers was poison oak as well.

Poison oak symptoms don't last long compared to an allergic reaction so hopefully that's what you got.

Sh!tty deal.