So sorry but there is no way I could tell you what is wrong. From what you are describing, it could definitely be an abscess and needs to be treated by a Vet. The infection could cause a lot of systemic problems if not treated. Add to that, he is obviously in pain. Part of pet ownership can be the expense of medical care. I see you wrote this a few days ago. Please send an update. Find or borrow the money. Most Vets will take Care Credit.
Margot is correct, your dog needs to see a vet ASAP. If it's a tooth abcess and it ruptures it can make him quite sick. Unfortunately, when our pets get sick, it is rarely a case of a quick fix unless it is something very minor like a small cut or scrape. It is always bets to have them evaluated by a vet because small problems can become giant issues if you just let them go. Your boy is obviously in a lot of pain from this so you need to act quickly and get him to the vet today. Just think of it as you wouldn't want to sit in pain with an abcessed tooth for days, so chances are your dog doesn't want to either, nor should you want him to. Please post back and update us with what the vet says.