Mental health

My mental health has been all over the place since I got pregnant. I don't understand whats going on. One minute I'm extremely depressed, everything in the house is dirty and I don't have to motivation to do anything, crying over everything, feel sorrow all the time over what life has become... next I'm full of energy, making 3 whole meals a day with dessert, cleaning everything, dancing with my child... what is going on?!?!?!