Root Canal? Pain on Left Side of Mouth

I have a question I hope you can help me with. I recently went to see my dentist because I had pain on the the left side of my mouth. It was pretty much my whole left side, top and bottom. It was very similar pain I had the year before on the right side, in which it was determined I had an infection and I needed to pull my bottom right wisdom tooth. That has since been fine. With my recent visit to my dentist with the left side she determined that I had an infection, but this time instead of pulling my one of my wisdom teeth on the left, she told me I needed a root canal on my #19 molar. I think she determined this because That tooth hurt worse than the rest and I could not eat any food with it. I ended up getting an antibiotic and within hours the pain was way less. By the next day my teeth feel perfectly normal, no pain, no sensitivity, and I can eat on that side just fine. My main concern I guess is if I really need this root canal because I do not have insurance and the procedure plus the crown afterward is very expensive. Is it possible it was just my wisdom tooth pushing on my teeth? Is it possible it was just an infection and the tooth is still alive? What would happen if I put off the root canal procedure and it turned out I really needed it, at some point would it be too late in the future to do it?