Pain in back of ankle when getting out of bed 3 days ago. now swelling and pain in back of ankle an up to knee. what could be wrong?

Many possibilities: You could have strained a muscle in your calf, or even a partial tear of a muscle. One major concern with calf pain and swelling is a blood clot. Get it checked out

Achilles Tendon.: It sounds like you have injured, strained or partially torn your Achilles tendon. You need to stop all activities immediately. Get ahold of some crutches and visit a specialist to evaluate the nature of the initial problem as well as any compensatory problems that may have developed since the initial episode.