My suggestions would be the same as Annie's, but would only add that if it's warm to the touch, you are nauseous, have a fever, or get streaks coming from it, get to an urgent care or the ER.
Can you see a doctor? It could be ringworm, cellulitis, a bite from a spider or something else, but the fact that it's getting bigger definitely merits getting medical care. If you can't get in to your regular doctor or a dermatologist, maybe try one of those urgent care places.