Can't Stand Too Long. Can't Walk Too Long. Pressure, Heavy

Can't stand too long. Can't walk too long. Pressure, heavy feeling in my legs and feet. Alleviated by putting feet up. I have arthritis in legs but that pain is different. I feel like I did when I was pregnant (3 times). Not particularly over weight. Feet n toes are not particularly cold. Past couple weeks feels uncomfortable when I sit (under garments and socks are not too tight )