21yo female. Nervousness feeling in stomach better by eating. Funny taste in mouth and dry mouth. Now stiffness feeling in knees after sitting.

See doctor. As described I can't give you a diagnosis of anything that sounds mortally wrong with you. Sitting for any length of time will give anybody stiff knees...so that doesn't seem to be terribly important. As far as the funny taste in the mouth the first question to ask is how is your dental hygiene and are you a smoker? You on any new medication? Dry mouth and nervousness go together as well.