What could cause edema in my feet?

Many possibilities. Some causes of swelling of the feet can include systemic problems such as hypertension, and problems with the kidneys and localized issues such as arthritis, infection, lymphatic obstruction, blood clots, varicose veins, trauma (fracture, sprain, tendonitis) and side effects to medication. Have it evaluated by a professional and get the appropriate treatment.
Many possible causes. Edema in the feet has many possible causes, so a doctor's evaluation will be needed to figure out the cause. Feet swelling can be due to malfunctioning leg veins, blood clots in leg veins, pressure on leg veins due to clothing or something else, heart failure, liver or kidney disease, too much salt, too little protein, sitting too long, standing too long, thyroid disease, tropical parasites, etc..