Ticks aren't just in the woods. A dog or squirrel could carry the ticks to your back yard. I'm really careful about it down here in Florida.
It could be a spider bite. Some spiders, like the recluse, can be quite nasty. I hope that's all this is. If you want to be sure, have blood work sent to Igenex Labs in Palo Alto, California. They are supposed to be the best labs to diagnose whether or not one has Lyme...the most accurate.
Sherrine