MacBook Air suddenly keeps freezing

I bought my MacBook Air new in September 2017 and it's been fine. This week, it's suddenly started freezing. It's ok if I'm just browsing etc, but it freezes up if I'm using Skype or FaceTime. The weird thing is that the video and sound carries on - I can still hear the person I'm talking to and they can see and hear me, but everything looks frozen to me. I can't click on anything or move the cursor. I just have to force the power off. Then it's fine until the next video call. I make all of my living on video calls, teaching, so I really need to fix the problem! My old Mac lasted ten years until it started to get issues!