Hi, antibiotics only deal with bacterial infections, not viruses, fungus or parasites.
Are yours larger than normal? Yes.
What's the cause of your "regional lymphadenopathy"? A biopsy should be able to tell that. But cancer is certainly not the only possible cause.
An ultrasound can give clues, such as the shape, the presence of the normal little bit of fat around the exit area (the hilum), the density, etc. Do you have the report?
Does a biopsy hurt? It's a relatively small incision and doesn't go deep. They more or less make a cut to expose the node, then lift it with tweezers/forceps and slice underneath it to free it, then pull it out. It's a simple thing and will set your mind at ease.
Are you seeing a regular primary doctor or a specialist. I would go see a Hematologist/Oncologist and let them see what is going on for once. This doctor sounds like a Quack. I always believe in second opinions no matter what it is.
I agree with Ken, and put your mind at ease. If it is something that needs immediate attention I would want to go get the biopsy ASAP.