Talk to Rheumatologist on Muscle And Joint Stiffness

I started having muscles and joints problems during pregnancy and it worsened after child birth with a C-section and epidural. I have been exercising and with losing weight the problems decreased but never got relieved. I also consume multivitamins and calcium supplements. Overall I am an active person. I don't have a sedentary lifestyle, yet my muscles and joints feel stiff and week. I can't lay down on my back or on my tummy. I can't keep my knees bent for more than few minutes. I don't know how to relieve this issue. Please guide.