How to treat complications of root canal therapy?

Hi doctor,

I got a root canal done on tooth, the one on the upper front left side. My dentist prescribed me antibiotics after my root canal for seven days. I took them for seven days. I woke up on ninth day with a swollen face on the same side of the root canal next to my cheeks. I went back to the dentist, and he took another X-ray and told me I had to take more antibiotics, so he gave m more antibiotics for another seven days. After leaving his office, I went to another dentist for second opinion as I knew something was wrong. The second dentist got another X-ray and told me the tooth my dentist did the root canal on was a baby tooth. My real tooth has been stuck in my gum for many years. He said some adults have this anyways. He also told me that the root canal done on my baby teeth was not good as they put inside the tooth after the root canal had been placed too high and now in my jaw. I am scared when I finish the second round of antibiotics; the infection will come back again. I wanted some help and suggestions.

Greatly appreciate your time.