Mine were so bad at the end I literally felt like my toes were going to fall off and if I knelt down it felt like they were going to pop it was bad lol
The heat and walking are not helping, but it could be your diet too. You are probably eating things you wouldn't normally eat, like yummy, delicious, salty, vacation food. The extra salt can cause water retention. The same thing happened to me when I was on a cruise when pregnant with Madeline. I know it sounds backwards but try drinking more water and decreasing salt intake and elevating feet whenever possible. Also, it's worth mentioning to your doctor. Sudden swelling can mean other things like preeclampsia. Hope you are having a blast!
