If you suspect your cat may have a broken leg, and/or a wound which is infected, he really needs to see a vet immediately. If your vet is closed today, he should be taken to a vet ER center nearby, or another local vet who has emergency hours.
What strength is the amoxicillin tablets you have and what was the dosage he took last time? What was the old injury for which he was treated with the amoxicillin? How old is the medication?
Here is a list of organizations which may help you find a lower-cost vet or one who might not charge you to see him, if you have extenuating circumstances:
and this one contains links to other sites:
It's very important that you have him seen right away, because if he does have broken bones in his leg, not only is he in pain (cats are masters of disguise when it comes to hiding pain), but the bones will not heal correctly and he will have a permanent limp which may cause pain for the rest of his life.
I hope you're able to find a vet who will help you out, because it's really important. You can even ask to pay out the fee in installments, so you don't have to pay it all at once, at the time he's seen.
Good luck and I hope his leg is treated properly so he can walk normally again and not have any pain!