Both opiates and gabapentin cause edema.

Low thyroid also... your med increase won't kick in for a week or two and then will be small and slow. Make sure you are taking that thyroid on an empty stomach with no calcium present.

Make sure you are getting enough water, and try elevating your feet after the work out.

Sometimes edema is minor and sometimes not. You have 3 factors predisposing to edema situations.

What supplements do you take? Can you list them?

Also make sure you get a good check up... cardiac and renal next visit to the doctor.

Cardio exercise increases blood flow, so you may have swelling in the feet from that...meaning the return is slower than the delivery of the blood to the feet.