Why is my Galaxy S6 getting hot when I use Internet while on data

[AC Question]

I've had my S6 for almost a year now, and battery life has been acceptable for most of that time. Lately, however, it's been draining insanely quickly (5% over 10 minutes) and getting unusually hot when I use data to access new or photos over the Internet. The problem doesn't occur when I access the Internet over wifi. I've tried a factory reset and a cache clear, but the problem persists.

If it helps, the heat is focused at the top of the phone, and particularly in the upper right hand corner, above the screen.