Why is my iPhone 7 overheating?

Hi!

For some strange reason my iPhone began to heat up much more than usual. It never happened to It before. I realized couse I started to feel it writing on the screen. In adition to the fact that the battery is quite degraded (79%) it started to drain dramatically. It went from 78% of charge to 63% in no more than 5 minutes, only using WhatsApp and Twitter, to the point that it warmed so much that It scared me, and almost burned.

I tried shutting it down, closing all the opened apps, taking the case off and nothing.

Doing any type of no intensive use, causes It to starting heat up, specially the area of the right of the camera.

PD: I don’t know if It affects, but a few days ago I bought a Macbook Pro, and they are constantly connecting, and even I used it to make phone calls. Also, is hot here, but no so much (22ºC) compare to past days, when It can reach 36ºC, but nothing happen until now.

What would it be? Should I formatting it? Thanks you so much for the time! And I hope I don’t disgusting you with my english!