I Think I Was Bitten By A Spider Or Stung

I think I was bitten by a spider or stung by something yesterday morning on the back of my hand. It hurt at the time but since become more painful and most of my hand is now swollen with limited range of movement. Should I apply ice/take Tylenol, for example, or is there something else that would help? I expected it to bet better with time, but it is considerably more painful and swollen than yesterday.