What the hell bit me?

Saturday night, I was at Dirty Girl's 30th birthday party. It was held at her father-in-law's place, which is right on the Milwaukee River. We were outside until the last hour, when we moved inside due to the mosquito population. I had on jeans and a short-sleeve shirt and added a hoodie when the wind picked up and it got a little chilly. This left my feet, which were in flip-flops, as pretty much the only exposed part of my body. While at the party, I had no feeling of being bitten or stung my anything on my right foot. I got home, got ready for bed, and the top of my right foot was a little itchy. Nothing really bad, just a little itch. I figured I got a mosquito bite, no big deal. That was until the middle of the night, when I woke up because my foot was itching so bad. After scratching it until I thought I might have actually broken through the skin, I managed to get back to sleep. Sunday, though, I woke up and the scratching the night before had taken it's toll, as the top of my foot was actually a little swollen. I put on some cortizone anti-itch cream and got ready for church. By mid-way through mass, my foot again was itching like crazy. I was trying to be subtle and scratch with my other foot when I could. By mid-afternoon, the swelling had increased and it was actually getting a little painful to walk from that. Also, the area that was itching increased. By Sunday night, it covered pretty much the right side of my right foot- from the middle of the top of the foot, down to the pinky toe and all the way down to the edge of the bottom of the foot. I started actually icing my foot to bring the swelling down. After careful inspection, there is no actual spot where I can see a bite or sting. Now today, I spent quite awhile scratching at work and then trying to ignore the itching that I felt. I had taken benadryl last night to get the itching to go away- no luck. After work today, I picked up some stronger cortizone cream- the strongest stuff I can get without a prescription. That worked pretty well in the main area where the itching had previously been. Now, it seems to be moving along the base of my toes along the top of the foot. Unbelievable. I have no idea what could have bit or stung me, but I'm hoping this will go away soon. At least without scratching as much tonight, the swelling seems to have gone down a little. Keep your fingers crossed.