Keep up the exercise regimen but make sure you take your oral supplements. My suggestion would be to try a different filler, one from a different family. For instance, you might try Evolence.
This is a collagen based filler and supposedly lasts at least as long as Restylane, according to the studies. Our rep tells us that it may last quite a bit longer, but that is a rep talking, as nice as she is, rather than scientific data.
You might also try Radiesse since this is also not a hyaluronic filler. It lasts longer than the hyaluronic fillers.
Why is Juvederm not lasting? You may not have received enough. If you told your physician that you only wanted one syringe, that physician might have tried to spread the Juvederm out evenly, not giving adequate amounts to the desired areas.
Restylane is running a special in which you receive a $100 rebate. Maybe you are degrading it quickly. I had one patient who had a terrific result for a month and then it diminished, much like your complaint. She came back and I placed another syringe and she was very pleased. So you might think of doing that.
Just speculation here, no scientific basis, but maybe your vigorous exercise regimen might increase your metabolism, and this might effect your Juvederm. Just a thought.
Hopefully, this will work out for you since otherwise you seem like a pleased patient, and that is what this branch of medicine is all about.