When is the absolute earliest post partum depression can occur?

I’m trying to be on top of it this go around. I know prenatal depression is a thing but I have been fine up until now, and I’m 30 weeks pregnant. I’m wondering if hormones just start going haywire in the last trimester or if I can develop prenatal depression at this point or if it could be post partum depression creeping in early. But I have had such a short fuse and have been downright just sad and feel burnt out dealing with my 3 year old twins lately