As pebbles says, you really should see a Dr.
Compression stockings are often perscribed. However, you should see a Dr first, firstly to exclude causes which can be treated more effectivly other ways, but equally importantly, you must get the correct size.
Too tight and you can cut your circulation.
In the short term raising your feet will help. If you can sleep on your back, then put a long pillow under your feet. When you st and relax, put your feet up. But make sure you support the back of your knees or you will put strain on those joints and regret it when you get to 40.
Do not take any medicines until you have seen a Dr. Those which help to eliminate fluid can cause enormous problems and you can become dependant upon them.
Do not, under any circumstances, cut back on your fluid intake. You would be astonished at the number of elderly women, especially, after being told, they are retaining water, cut back on water, get constipated, become confused and end up diagnosed with dementia, all for the want of a good s**t.