My little boy loves MIL more than me ☹️

Shes taken my little boy away from me. In feb i went back to work 4 days a week and she looked after him. (We live with the mil and fil), and Ive just had another baby 2 weeks ago so he was with her whilst i was in hosp for 6 days. (First time i left him) . My boy who is 22mo is obsessed with her. He will cry every-time shes out of sight. He only wants her when he’s upset. He even started to call her mama! And she doesn’t correct him. Im so heartbroken and i haven’t stoped crying today or this week. Im really trying to connect with him and make sure he knows that im his mum but how when shes around him every single min. Feels like i failed as a mum and no one understands. How and why is he obsessed with her. He should be having separation anxiety from me not her!