Talk to General Physician on Leg And Knee Pain

I have a 1.5 year old baby girl. And it's been 2 years of my marriage. Ever since getting pregnant,I've been having severe pain in specific areas of legs.. Whenever the activity of legs increase, the pain increases. I started mild body workout from the last week. Since then, I've been going through excruciating pain in my legs again.. When I take rest, the pain is relieved but with exercise n activity, starts again. Walking up the stairs also cause pain in my knees too.. My calcium level is normal. I have not gone for Vitamin D level testing as I don't have pain in any other parts. What could be the reason for this? Any tests required? What should I do?