Why do I keep getting major fluid build up/swelling in my cheek every few weeks?

Based on your story it may happen that first implants and later fillers and hyaluronidaze created a condition known as chronic seroma. Direct surgical exploration of the area of swelling (cyst) and/or aspiration with analysis of aspirated fluid  may help. Ultrasound or MRI of the face when pocket is full of fluid may be considered. Good luck.

It is possible you are having occasional fluid build up inside the capsule of your old cheek implant. Any implant forms a capsule around it. Scar tissue that can form a contained space can easily fill up with fluid and the amount of fluid may vary slightly from time to time. It is difficult to remove this scar tissue so it is also difficult to keep this swelling situation from happening. One technique is to drain the fluid regularly, which may require the help of ultrasound. If the capsule/seroma can stay collapsed long enough, sometimes it will go away completely. None of this is terribly easy, so you may need to decide how much trouble you are willing to go through to address the swelling issue. I hope this helps!