A.H.
I second other mom's advice-- you should see your doctor.
Also, are you sure you're drinking enough water? UTIs and pre-term labor can all be exacerbated by dehydration. It's really hard to stay well hydrated when it's been so hot, but keep drinking-- more than you think you want.
Also, the same company that sells "Emergen-C" also makes an electrolyte packet. For a small price, you just empty the packet into a liter of water and you have instant gatorade without the sugar, artificial colors, and expense. It's especially important to consider something like this during heat waves when you may be sweating a lot and losing salt and minerals. If this idea doesn't appeal to you you can also try diluting fruit juice with water. When I was pregnant last summer I started drinking apple juice (relatively low sugar content) and water mixed 50/50. It's surprisingly refreshing and I still go for this today.
Take care of yourself and good luck!
A.