It gets hotter than that here, hydration is probably your issue and water is key to fixing that. you also may be overworking yourself. my first couple of rides out I was wicked hot but quickly learnt to pace myself, now I spin most of the time and have no issues. also you need to cool down after wards and by that I mean when you get close to home or when you reach your neighborhood go around the bike at a nice slower pace than usual and drink plenty of water after.