iPhone 7 heats up quickly

Hi

I have been using iPhone 7 since Sept 2017. I have observed that the phone heats up very quickly with short(5-10mins) use of video calling, Maps, watching YouTube etc. Though the activities are continued for very less time e.g 5-10mins, but feel the heat on front and back surface, which is very disturbing. If I get call immediately then it's difficult to continue with as I can feel the heat while holding the phone near to my ear. I am using iPhone for the first time. I have not faced such issue with my earlier non apple phones. I tried Factory reset, but that didn't help. Please help.