My Dog Has Been Bitten By I Think A Spider Or A Wasp, His Paw Is Swollen X2 Or 3 For 1.5 Days, What Do I Do?

My 80lb dogs paw became swollen 1.5 days ago and appears to have been bitten, he was a single puncture mark the size of a pin top that is weeping pus like fluid between his toes on the top of his front left paw. The swelling came on within an hour & has not decreased in size in 1.5 days. I think it is a spider or a wasp, what should I do. He has not been sick & has been eating fine but does not want to put weight on it. What should I do?