A medical person would begin by asking you some history questions that may help point out possible causes. Your position on the bike may be fine but if you have recently increased mileage beyond what you typically ride, this would suggest an over use injury. If an MD is unable to find a source of the problem, I think your best course of action to be to analyze your own self. For instance, does your leg track straight up and down or does it flop in and out. In this case a tapered shim in the shoe would help. Or, see that you are sitting squarley facing forward and not twisted to one side which may cause one leg to work more than the other. These are issues an competent fitter would spot and correct.

If I've put in a hard day I may feel some soreness a day or so later which is normal and will subside in a day or two. I massage such soreness with this.Tiger Tail Rolling Muscle Massager | Free Shipping at L.L.Bean There could be various solutions for you, including better fitness or a better bike fitter. You need to probe possibilities.