ONLY swollen ankles(no feet or legs)

Marisol
Question?
Yesterday when I got home from work I took my comfy shoes off as well as socks. I've noticed my ankles where really puffy/swollen. So my question is could it be a sign of preeclampsia? I never had it with my son. Also I know you can get swollen feet and ankles later on, which I did with my first 2-3 weeks before his due date. Never this early. 
Or could it be...
Water retantion? too much salt?
FYI: I worked 16 hours yesterday, which I am used too. Out of those 16 hours I am on my feet  about 13 hours(moving/walking around). 
Thank you!