Well, you can go outside, but it is awful. The worst place I've ever been to is Kuwait in August. 100% relative humidity and at least as hot as 50*C in the shade. Ugh. I hope that at least the RH is lower where you are.

I would recommend starting with magnesium citrate, or a magnesium complex. There are quite a few bioavailable forms of magnesium. Citrate is one of the easiest to absorb. Many humans are probably deficient these days, and since it's water soluble, it's exceptionally hard to overdose.

Swimming is always good!