Hello!
Recollect if you had any fall or injury. If it is an acute condition it is sure linked with some injury, infection or allergy.
Take symptomatic relief and apply ice packs and NSAIDs.
Take an appointment near an orthopedician and take it forward.
Take care!
I'm sorry to hear this. I think you should go see a doctor ASAP. "Grossly swollen," - that needs to be checked out.
I hope you feel better soon.