Are you riding in work clothes, or do you change into shorts and a t-shirt, bicycle clothing, etc.?
I have a similar problem in the Fall here in New York. In the mornings, I can pretty much wear my work clothes on the bike and not be too sweaty when I arrive at work. But in the afternoons, the temps can soar and the long jeans I was wearing on the morning commute now feel like an electric heating pad.
Try bringing separate clothing for the ride. As far as the hills, my first suggestion might fix that, too, as looser clothing makes riding, in general, a lot easier.