Screen stays on during call

What's up all? Recently my phone has not been turning the screen black when held close while on a call. Obviously this is annoying because I have to keep it away from my face to keep it from pressing the screen and hanging up/muting/etc. Any idea how to fix this or what the cause was?

No, there is no case covering the sensor... I even put my hand over the sensor on a call and it doesn't go black.

Thanks!