at what gestation can your feet start to swell and get sore?
Any but more common in the third trimester. If the swelling is sudden and a lot or you're having other symptoms with it it could be pre-e.
If it is as hot and humid there as it is here I don't even think you have to be pregnant to be retaining water! :P
Just keep an eye on it, as PP mentioned, if you have other symptoms could be more serious than a little swelling.