If you already have a filling can you possibly have a cavity on the same tooth you have a filling?

Yes: Filling replaces the part of the tooth that was damaged (infected). It does not protect any other part of the tooth. Please have new cavity fixed ASAP, delay can only allow more tooth destruction. Also discuss with your Dentist brushing technique, floss or Water Pik use, diet, choice of toothpaste, fluoride, snack-food choices, etc.

Of course: It is possible to have another cavity because every tooth has 5 surfaces.

Absolutely: Just because a tooth is restored once does not mean it will never need another restoration.

Yes: Yes, you can still get recurrent decay around a filling or on other parts of the tooth that are susceptible bacteria and the acids found in the mouth.