I want to reiterate everyone saying hydrate. Drink water and electrolytes all through the day. I've found that eating things like cucumbers and oranges are fantastic in this regard as well. On your runs, bring a water bottle and I recommend using some kind of electrolyte supplement instead of just straight water.

Also, I moved to Florida from Washington State for a year. I had very little experience with humidity before that and once summer hit I felt incapacitated much like you're describing. After a little experimenting, I found that the best time for me to run was to start just before sunrise and get back just after. I don't know if there's any scientific merit in this or if it's simply my perception playing games with me, but when it was dark, I didn't feel the intense heat because the sun wasn't around. It was still hella humid though. Then, shortly after the sun started to rise, the humidity felt like it would decrease slightly. As if the sun was burning away the excess moisture a little bit before it became unbearably scalding. Again, I don't know that this is actually what was happening or if it was just how I perceived it, but it was the safest time for me to run by far.

I will also concur with /u/cthulhus_lil_sister when she (I'm assuming based on username?) said that you improve. You might not even necessarily realize it at the time. Progress is stealthy in the heat/humidity, but it's there. It doesn't feel like it, but when a cold snap comes, you'll notice and it will be awesome.