If you're in the UK I would ring a chemist, and ask to speak to the pharmacist. Boots is usually a good one to ring. I don't suffer from knee pain, but suffer with neck pain from a car accident. I use heated gel packs, or a hand warmer. When it gets unbearable I take Veganin, & something called sleep aid (to mimic what Syndol used to do), but I wouldn't advise you to take any tablets without speaking to a pharmacist at least.
I've had one bad knee (cause unknown ) on and off for over 30 years and the other for 10-12 years, and they are worse in wet weather. I've been taking glucosamine/chondroitin tablets for many years (pre diabetes) and it never occurred to me to stop when I was diagnosed with type 2 about 16 months ago. There's some debate about whether these tablets actually work, but they certainly help me! But I noticed too when I went on my low carb diet that that also helped and my joints were more flexible- but it may have been weight loss related.