I have been taking this drug for about 15 years and this past year I still feel the old depression seeping in. The Dr. upped my dosage but I feel no different. Is this because I am just getting old?
Absolutely. In the case of medications, it's called building a tolerance.
Prozac is infamous for this, so infamous that a tolerance to medications has been nicknamed "the Prozac poop-outs."
Please discuss this with your doctor. It may well be time for a different medication.