The jaw muscle (Masseter) is divided into two distinct parts, the superficial and deep. Occasionally, due to various reasons, the injection may be placed too superficially and fails to diffuse to the deeper portion of the Masseter muscle. During chewing or jaw clenching, this untreated deep Masseter may herniate through the weakened superficial layer during contraction and cause a visible bulge.
Fortunately this can be remedied. I suggest you return to your doctor as he or she is the best person to know how much and how deep the previous injections were.
Hope this helps.