Partner going back to work after having baby and I’m so anxious

I have a 2 year old and now a 4 week old. I’m breastfeeding so I have to do all the night feeds. The baby doesn’t go into a proper deep sleep until around 12-1 am. She’ll sleep for a couple hours, waking up any time between 3 and 5, and after that she’s awake every 2 hours wanting to be fed.

Lately my toddler who is in her own bedroom has been waking up sometimes at 3 am, and is up for a few hours playing and goes back to sleep, or she’ll wake at 5 or 6 and comes into my room wanting to be up for the day.

It’s been exhausting but my partner has been at home and able to help out with the toddler situation, but when he goes back to work on Monday I’m going to have to deal with it all myself. I’m so anxious because I honestly become psychotic without sleep and I don’t know how to get my toddler to start sleeping at normal times again.

On top of this I’ll be expected to keep the house clean, laundry, cooking healthy food for my child. I just feel so overwhelmed and scared. My partner often works late too so I really don’t know how I’m going to do this.