Botox on Masseter - how can I get this resolved? (Photo)

Been doing Botox to slim my jaw since 2016 (every 3 months, total 45 units). Initially I used to get crooked smiles but over the years it disappeared while doing the procedure. Last year, I noticed that the slimming effect started reducing compared to earlier years. After the one I got done in November, my jaw slimming almost stopped. I got another one done in March. I feel weakness in my jaws while clenching but no slimming effects at all. What could be happening and how can I get this resolved