I have been freezing bottles of water overnight and then I have ice cool water as they defrost throughout the day!
I find that really helps to keep me cool.
I'm lucky that i'm at home so I wear lounge clothes, and vest tops and t-shirts, but I can sympathies (sp?)
as I worked in an office with my dd but I was only a couple of months and it was no fun!
Iced water will most defiantly help you out!