Battery Problems, 3% then shuts off

Hello everyone, I am a slight bit of an Apple groupie, but lately I have had a few minor problems with my iPhone 6s. First it started to bug out and lag, all I would have to do is restart the phone then it seemed to work again. But the. Just the other day my phone would start clicking different places even though my fingers weren’t even near by. Then the phone wouldn’t charge ): It went black for several days until I finally realized that the red battery simbol would show up after several minutes of being charged. The phone will **sometimes** get to 3 percent, looses battery while still plugged in (with authentic apple cord and block) and will then die again. It’s really weird and I can’t use my phone? Thanks for any and all help.