My macbook Air is making fan noise

Two days ago, I was watching Netflix in the morning before heading into work. I close my laptop and left. When I came back that night, my laptop started making a fan noise and it wasn't loading anything. Last night, I had updated it because I had thought it would maybe help. It now loads the internet, but it runs very slow. I can't watch a video without it jumping and it doesn't give a clear picture. Thing is, my laptop isn't overheating at all. It's just making the fan noise and I have no idea what's going on and how it started acting up when it was absolutely fine that one morning. Anyway, if anyone has some insight on this or tips to help me fix the problem, that would be great!

Also, I've had this laptop for about 3 years exactly.