I'm 37w4d and my ankles used to only swell by the end of the day too, now I wake up with swollen ankles & feet and it hurts to even walk. Putting my feet up doesn't help me.
I heard it could happen around that timeframe. I'm 23w and have been elevating my feet daily for at least 30 min, drinking lots of water, cutting down on salt and sodium and exercising to help prevent it. Have you talked to your doc?