We say this every year as the temperatures rise in "Famously Hot" Columbia, SC: Be hydrated and stay cool.
Your body needs time to acclimate to weather changes. For most of us, up to two weeks. But being in a controlled AC environment for the majority of the day and then jumping into the outside heat to workout is never going to be an easy transition.
The main thing is to always be hydrated. This is a no brainer. Or should be.
One way to help adjust your body on a daily basis during those hot and humid periods after being in an air conditioned environment at home/work/school, is to drive to the gym with your windows down.
You can still have your AC on if you like, but letting the hot, humid air hit your skin on the way to the gym will help your body adjust to "cool off" quicker versus walking straight into a wall of heat with a 20 to even 30+ degree temperature change.
Your muscles expel heat to the surface of the skin through convection and drawn to the surface through your sweat, which then evaporates and cools the body. When you exhale, or even use the bathroom, you dispel heat as well.
When it is hotter than your skin temperature though, your body is unable to cool off through regular convection or radiation. Your body's sweating and evaporation becomes the primary cooling mechanism during these hot and humid times.
A smaller person will typically lose heat easier as they have a higher surface to body mass ratio, whereas a larger person will expend more energy at the same exercise levels to lose the same amount of heat.
We always say, "you are the king/queen of your castle", you know how you feel. If you're struggling to adjust to the heat conditions, take it a little easier until you can adapt. If you need to "take a knee" or sit it out for a bit, it's perfectly fine.