I am sorry Zachary has this problem.
It is likely he has either cut the pad or been in a fight and it is a cat bite. Both will cause acute pain and swelling with the potential for infection to develop.
It is usual for cat bites to develop into abscesses, so a large swelling containing pus develops, this often casues a fever and so cats will often become lethargic and depressed and possibly anorexic. If persistent this anorexia can cause further problems,
Pain and swelling will respond to anti inflammatory/pain killer medications. Unfortunately cats are very sensitive to these drugs and human versions (paracetamol and ibuprofen) are lethal, so specific ones which are licensed for cats are needed. It would also be wise for any develping infection (discharge, heat or redness) to be treated with antibiotics. So ultimately a veterinary exmaination is required. there are many vets open over the weekend and some of the corporate chains will offer a free first consuiltation if you are newly registered so you would just pay for medications.
In the meantime, bathe the foot/wound with dilute salt water (teaspoon of salt in a pint of water) and try a cool compress on the paw to help with swelling. Do not put ice directly on to the paw, wrap it in a towel.
A veterinary examination is also important to ensure there are no breaks or injuries elsewhere.