Why is there pain in filled teeth?

Hello doctor,

About a month ago, I got a filling on one of my front teeth, they called it a surface cavity but filled it like a normal cavity. For the first two weeks, I could barely drink room temperature drinks without being in agony. I made an appointment after two weeks to have my dentist look at it to make sure it was not cracked or anything. He never even looked at it, he gave me an antibiotic and said if it did not get any better, I would need a root canal. A few days later the sensitivity went away and I thought it healed. Last week, I noticed the gums above it have changed color. They are a slight red, purple and the gum itself is very sensitive. Under my nose and some of my cheek, I can feel where it is swollen (the gum). It also throbs sometimes. Should I take the antibiotic that my orginal dentist prescribed or should I just wait it out until I see the new dentist to see what they say? I am just scared. Is it an abscess and I do not want it to become more infected.