swellin on shoulder, does it sound like a sting?

[beaconhorse]

After him bucking me off on sunday..........I didn't take much notice of him yesterday as my RA was bad. But today on his shoulder and going down a bit is a large swelling. It is a little warm but not much. It actually looks so big at first glance you would think he had dislocated his shoulder. However he is perfectly sound, happy to bend his nose anywhere including nearly onto his withers. It doesn't seem sore anywhere just BIG.

Looking back to Sunday before I rode I actually commented to my friend that there was a wasp around me most of the time

Does it sound like a sting? If not any ideas?