How long does it take for a sore/infected tooth to become fatal?

I've had problems with a sore tooth for a couple of years now, but it's recently started getting worse. I couldn't see a dentist because I was unemployed and uninsured, plus I didn't qualify for any kind of state aid. I finally got a part-time job recently, but it'll take me a while to save up money for insurance. The tooth is usually just sore, mainly after eating sugary things like you'd expect. When I got fired from a different job last week (yes, fired and hired in 2 days), I think I was grinding my teeth in my sleep due to stress because the pain was dramatically worse. I started rinsing with peroxide after meals to in hopes it would help the pain/infection somehow. Today, though, the tooth itself isn't bothering me. Instead, it feels sore near my nose and left cheek, and I have something similar to a congestion headache (pain and pressure when I lean forward or bend down). I'm starting to worry that whatever infection I have has spread to my jaw. I don’t have a bitter taste in my mouth or any open sores, but he gums around the tooth feel sore and tender. When Dentistry from the Heart came through my hometown 2 months ago, I went to see them. They took x-rays before treating a different tooth and prescribed me Amoxicillin. I've heard/read horror stories of people who went too long without seeing a dentist for an abcessed tooth, and it eventually killed them. If the tooth I'm talking about were potentially fatal, the dentist would have operated on it, right? Also, would the antibiotics they gave me possibly helped/delayed whatever infection I may have? I feel like I’m asking a lot of questions, but I’m really worried.