As @Coloma mentioned, it sounds like it could potentially be a DVT. You need to get this checked out soon. If you feel it ascending (going further up your leg) call an ambulance and get into the ER right away. A DVT can break loose and shoot up your lungs causing a pulmonary embolism which can easily kill you.
I don’t want to alarm you, especially becaus there is probably a very good chance this isn’t something serious, but I did want to make you aware that you need to get it checked out soon to rule out a DVT. Again, if you feel the pain rising like a clot moving up your leg, then you need to go to the Emergency Room right away.