What Causes Back Pain Near Joint And Pelvic Region After Delivery?

Hi Doctor

I have given birth to a baby gal and she is 2 montsh old now. I had a normal delivery, but i had back ache before pregancy and after delivery i have been experinecing back ache near the joint and pelic region. And at time i can feel my stomach heavy. i asked my gyanxe said it will go after 3 months but i dont see any improvemnt., i fell once i couldnot even lift my leg