I can't come up with anything that looks like that an causes instant pain, either from nettles, thorns, or sap. I kind of go with So Lucky, was some other plant growing in there that you touched? Or did you touch a stinging caterpillar? We all have different allergies and reactions so it's kind of hard to judge just by your reaction, two days of pain, but I've had some really instantaneous pain with stinging caterpillars.
My suggestion is you very carefully take a piece of that to your county extension agent and get them to identify it. Include bark, leaves, any flowers or seed pods. If they can't find anyone local to identify it they should send it to Urbana-Champaign. Identifying plants is something the extension agent should be able to manage. They should also have a recommended way to control it.