I lost a lot of weight after giving birth.

I was 141lbs before pregnancy, 168lbs at 9months pregnant and 1.5 years postpartum I weight 125 lbs and it's going even more down... I don't know what to do. All clothes are big, I never wore xs? Should I visit a doctor?

How do I put on weight? I eat, not a lot, but I do eat normal, meat and milk. Everything. Anyone had this problem?