Why is it so hot at night? I've tried everything and I'm still always far too hot in bed.

I know in England we always complain it's too cold or wet but this summer it's been a heatwave for over a month. I'm loving the heat in the day time, most of the time however at night our room is so hot. Me and my husband have tried everything from cool water bottles to fans in the room but I still find myself hot and sweaty in bed.