Congrats on being down 20 comrade! I think that as far as exercising goes, walking should get easier and easier on your joints as you lose more weight and gain more muscle in your legs to compensate for the pressure on your knees right now. It makes sense if you’re just starting out that they might be giving you some trouble, but i think a doctor would probably assure you that walking is still overall a good low impact form of exercise despite the joint issues you’re having. Listen to your body and if you’re feeling a lot of pain I would go easy on them and try other exercises that are even lower impact but ultimately it’s something that your body will learn to adjust to. Not a doctor but I do have joint issues as well and I find that just starting out any type of exercise feels tougher on my joints than it does once I’ve got some muscle built up.