I get swollen feet and there seems to be no rhyme or reason. Sometimes they swell when I've walked for miles. Sometimes they swell when I've not walked much that day. Some days they don't swell at all no matter what I do. I try to drink a lot of water and that seems to help *some* of the time. I've been seeing a podiatrist for 2 months, since I also had an infection (since cleared). Low-carbing for the past two months has seemed to reduced the incidents of swelling somewhat.
Every night I inspect my feet, and massage them with cream prescribed by my GP. I also never go without socks and shoes or slippers, and wear very roomy, comfy socks. Check that your shoes are fitting properly (feet size can change!). Elevate your feet when you can and try to drink more water. Other than that, your GP may have some ideas, and may refer you to a podiatrist.
Have you had a routine foot check yet?