As long as you are in good health generally and do not have a fever, there should be no problem with proceeding with your injection. For a simple bladder infection, some doctors may even treat for 1 or 3 days to render the urine sterile, which means the germs are killed off and no bacteria grows. You don't mention how many days of treatment you have had or how many have been prescribed but chances are good you should have no problem.
Absolutely I would postpone the Bellafill injections until you have completed your antibiotics. The procedure is completely elective and you must be in optimal health to undergo any elective procedures. You are at an increased risk of infection because sometimes the bacteria gets into the blood stream. The bacteria can then be trapped in the Bellafill and cause a biofilm infection. These are exceptionally hard to treat in Bellafill clients.