Whats Happening To My Skin?

So i havent really noticed it until about 2 years ago that when i get under the sun for a period of time my skin will get like really burnt looking red, and people tell me it feels hot. its mostly on my arms, chest, and legs, but i dont see it on my face because i wear makeup... but its weird like i'll be sitting outside at lunch at school and the sun is out and i'll turn bright red and people will tell me about it but i dont notice until i look in the mirror. my teacher even confronted me about it and asked me if it was sun poisoning or maybe a new lotion i was allergic to? but it doesnt itch or burn, and its not a raised rash, its just really red. if you could help me out thank you in advance, but thanks for reading this anyway.