Pain while walking

I believe that is a normal response in a muscle that is not "used to" being exercised. As we exercise, we are using a lot of oxygen and glucose allowing our cells to undergo aerobic respiration/metabolism. As we continue to exercise, our need for oxygen increases because our muscles are contracting so hard they are quickly using up a lot of oxygen and glucose during aerobic respiration/metabolism. As this process continues, our cells may get to a point where there is a deficit in these two, which causes a switch to anerobic respiration/metabolism, causing the production of lactic acid, which is the BURN that we often feel in some muscles during exercise. If you stop and rest, you may notice that the burn goes away as the lactic acid is cleared. It is a normal reaction and as our muscles grow and are re-modeled and we are able to better oxygenate, you will be able to work out for longer periods of time without feeling this burn.

Muscles also fatigue and hurt from overuse or doing too much too soon! I would also suggest that if you are concerned or if something just doesn't "feel right", definitely go see your physician! Hope this helps! :-)