If I have a fever and am on antibiotics am I still contagious to an infant?

It depends... It depends on which infection you have and how long you've been on the antibiotic, but it's probably safest to avoid contact with infants until the fever is gone. Talk to the doctor who prescribed the antibiotic for your infection to know for sure.
Hard to say. I have no way of knowing if your illness involves a virus or bacteria you could easily spread to the infant. Having fever is a realistic sign you are potentially contagious for most germs. If this were just strep throat & we know that a day on meds stops the spread, but you could also be carrying a virus along with strep. I would avoid contact until fever free 24 hrs.
Yes. Most feel that while a fever is present the disease process is still active.