Mine does the same, but both get swollen. However I am on my feet all day at work. I started using those circulation socks and they have helped. My ankles don't get as swollen and my feet don't hurt as bad. I also make sure I put my feet up whenever I am on break or at home.
I have varicose veins and had to get an ultrasound my last pregnancy for blood clots too. Luckily nothing. This time around my leg is swollen but not as painful as my last pregnancy. Good luck to you. I hope they don't find any!