What Causes Red Rashes On The Face?

hello, i'm having rashes on my face right now, forehead, cheeks, nose. Very red just after bath, red after 2 hours but still noticeably red. It's not actually itchy(just little to nothing, but when i start to touch it then it becomes itchy), my face is greasy(but ever since i was younger it was already oily), and there are scales. I think its is seborrheic dermatitis but i could remember that this month my classes started and I was always outside, exposed to the very hot climate. Last month I was just staying in my air conditioned room and it is seldom that i go outside. I noticed too that when i'm exposed to the hot climate, my body is sweating real hard while my face is just oily, which I think is wrong because if my body sweats so hard then my face should be at least 50% as sweaty. So it may probably heat rash? But it may probably be allergic reaction because i changed soap the time I'm already going to school, because Dove is so greasy that dirt and pollution stick to my face when i'm going to school, so i changed it into something with more soap in it than the moisturizer which is Palmolive. So what do you think it is? Sorry for my bad English. Thanks or your time.