My niece doesn't just do this with her parents, my parents get included in this aswell! My sister and niece are at my parents at least 3 days a week (often from 10am until after dinner) and my niece has gone through periods where it's all about Pa and Pa has to do everything, and then it switched to being all about Nanny which obviously makes things hard for my sister when they're at home and not at Nanny and Pa's. Even though it's just for the day, there are times when I visit and I'm the favourite.

It must be so hard, especially if you've been dealing with PND, but from everything I've seen this is totally normal and soon your DS will go back to it being all about mummy.