I was driving my car yesterday, when I felt an intense sting/pain on the upper part of my thigh (close to my groin area) like having a needle injected. I pulled over thinking an insect must be inside my pants. When I checked there was no insect but I had a hard lump the size of a quarter on my thigh. It was red and turned black and blue. This evening it is two inches in diameter, black and blue, but the hard lump is gone. I've never had anything like this happen before. Could it be a broken blood vessel or a blood clot??