Yeah, I learned that the hard way - Pigeon pose doesn't hurt when I do it, but I can barely walk the next day. I can't do squats either - but this is directly related to the exact injury! Interior / Exterior ligaments, cartilage damage etc. are all going to be different. However, it sounds like your dr. does not think that anything that major is wrong. Look up knee strengthening exercises online and of course talk to your dr. first!