No energy poor appetite

So I’ve noticed ever since I had my son April 2019 I’ve been constantly feeling like I have no energy at all like no energy to wanna get up and do anything. I Same with motivation I just feel like it gets worse as the days go by. I’ve lost 20 lbs since 2020 started and just can’t seem to gain weight it makes me so insecure. I need some opinions on what I should do