What would make my feet swell?

Lots of things from heart failure to thyroid problem to bug bites. You get more from this site when you provide detailed information on how a problem became evident, other symptoms, past efforts to get evaluated or treat. You are welcome to start over with more data. It may just be better if you go see your doc.

Most commonly venous insufficiency, but otherwise too many possible sources to count including heart, kidney and liver conditions to name a few. Some prescribed drugs are also notorious to cause swelling or edema.

The common causes are congestive heart failure and venous insufficiency. Other causes are protein loss in the urine and intestine. Low blood proteins due to poor nutrition. It would need physical examination to ascertain the cause in the individual person. Wish you good health!