I woke up this morning with this on my leg. The red is where there were some bumps that I scratched and it has been red like this for an hour now. The other small bumps are what they looked like before scratching and then there is the large red mark on the skin as well. I'm not sure what the cause is but everyone seems to think bites or an allergic reaction. I'm just not sure where either would have come from.
Some resources that may be helpful with your rash identification are provided below: