Proximity Sensor problem with my Samsung Galaxy J3 2016

I have a Samsung Galaxy J3 2016 with android 5.1 and whenever I receive calls, the screen keeps flipping on/off. I guess my proximity sensor is busted ? I also didn't see anything in my settings regarding that. Is there any way for me to have my screen locked all the time during calls? Sometimes I press buttons on accident with my face and it ruins the call. Thanks for the help!