Hi. My Thighs Hurt When I Walk. I Am Moving

Hi. My thighs hurt when I walk. I am moving slowly today. My legs feel stiff. I clean cars for a living. I have had this problem before I started working cleaning cars, but it usually the right leg only and today it is both legs. I am a 45-year-old female. I take meds every day for bipolar disorder. I usually write the stiffness off to getting older, but I am wondering if I should see a doctor. Thanks.