iPhone overheating? Also my display is glitching

I have recently purchased an iPhone 7 battery from ifixit, receiving it today I cracked open my phone (as I have many times before) and paced in the new battery. I began to notice some things when I felt my phone was extremely hot, I had also noticed that my screen sometimes glitches and shows 2 images and inverts the color (though touch was just fine). I have no idea what the problem is if there really even is one and would appreciate help on this.