swelling advice

I'm 36 weeks pregnant with a big baby (currently estimated at 8-9 pounds) and over the past several days I've been having increased swelling in my feet and ankles. If I sit too long at work, my lower legs will also swell. Is this normal? When I elevate them above my heart it goes down mostly. Any tips for managing this, and/or should I be concerned and contact my doctor? Thanks for your help.