What Can Cause Leg Swelling This Has Been Happening For

What can cause leg swelling this has been happening for over a month now? I can wake up in the morning and my legs are completely fine, but by the end of the day my knees down to my toes are so swollen it is hard to walk sometimes. I would like to know what could cause this to happen.

I can not afford to pay for an answer to my question, I am retired and on Medicare and my funds are limited. Thank you for trying