I'm a beginner with running but I'm so far pleased with my progress and can see my stamina building after a month - having not ran since before having my two children over 5 years ago I've gone from being able to manage 2k to being able to do 5k in about 33 minutes. I'm really enjoying it too - I started because I wanted to do something for my mental health during lockdown, juggling WFH, homeschooling and a toddler 
However my knees have started to hurt! It's just an achey pain. After a couple of days without running it goes away and then it's back after another run. I stretch before and after. Any tips to help? I really don't want to stop and spoil my progress!