Small S7 problems

[AC Question]

It's a bothersome one but when I have anything held on the touch screen [stylus, finger, assorted fruits] for more than 2-3 seconds the screen begins to change between brightness getting more sporadic and servers the longer I hold it and it begins to bog down the entire phone where all the apps and even the UI begins to lose frames and performance. But when I stop resting/holding my finger on the touch screen... poof! Back to normal. But if I hold it begins to do as I explained above. Can anyone help?