I had very bad fluid retention in both pregnancies, and it actually made my skin hurt! Between that and my hips, I had a lot of trouble walking.
In my case, I did have some health issues - high BP in my first pregnancy, and in my second pregnancy, diabetes. That said, none of it was life threatening, but my OB kept a close eye on me (I also had a heart specialist in my first pregnancy). I had regular urine tests to check for protein.
When I suddenly gained a few kilo's in less then a week at 37 weeks in my first pregnancy, my OB decided to induce as she was worried about pre ecclampsia, so I would definitely contact your doctor and discuss it with them. It could simply be normal swelling due to late pregnancy and hot weather, but best to be safe.
I did have the swelling in pregnancy number 2, but no high BP, so my doctors weren't as concerned.