Daddy in control / pretty sure it's PPD / hopeless

I am a young Mum. I fell pregnant really unexpectedly and at a huge point of transition in my life - I'd just graduated from University.
My partner is quite a bit older than me, he had a son previously who sadly passed away about 4 years ago.
He was so happy when we found out about baby, and I felt that it was the best thing I could do for him cos he 'deserved' another shot. He was a single Dad previously so it made me think that this time would be easier being the two of us.

Now I am working again, I have a really demanding job, which meant I had to return to work when my baby was 5 weeks old. He is now 8 weeks old.
I have some comfort in knowing that he is at home with his father and they are literally 2 minutes drive away. Except it doesn't really comfort me. It doesn't please me either. It doesn't seem to bother me either way.

For me being a work is easy. I don't have to think about them or myself at all. I just work solidly from 8:30am in the morning til 6:00pm at night. No breaks, just work. Going home is hard. I feel like I put on a fake persona when I'm with baby and daddy. I eat, bath baby, feed him and he's off to bed. I'm not far behind him these days, I'm exhausted. My partner and I hardly talk - we do the basics, 'how is he' 'how was your day'. We seem to both put our son in between us so we don't have to talk. We just focus talk elsewhere.

These days baby responds more to Dad - I knew this would be the case cos he's with him all the time and only with me for a few hours a day. It just adds to the feeling of disconnect I have with my baby. It builds up the wall between us ever higher.

Today I took the day off - my first in 2 weeks. My partner pretty much tells me what to do and when to do it. For instance, I was taking my time, trying to get my baby to smile while changing his nappy and he took over cos I was being too slow. I know he has developed the routines with the baby and spends all day with him but this behaviour makes me feel so unwanted and un-needed. When I try an express my feelings to him he tells me I am 'being selfish' that its not about me it's about our son.

So I guess it just adds to my disconnect, now I feel like I'm trying to maintain the disconnected feeling - just to make it easier. I don't react to his crying anymore. I try and leave in the morning before he is properly awake so I don't have to deal with him. I feel these days like I have to ask his permission before I do anything with my son.
My partner and I feel so separate now, but he doesn't seem to notice or maybe he doesn't really mind. He has another son. I worry that maybe he is trying to recreate what he had before?

My partner keeps talking about the next baby, I don't even want to entertain the thought of another baby. To me getting pregnant again will feel like a service to my partner. "A job" that needs doing instead of the joy that it should be. I also don't want to do all of this / feel all of this all over again.

I've never felt this way, I get so angry with myself but I just can't shake it so I just go into 'standby mode' it's like I'm here but not really. I thought PPD occurred soon after birth, but I've read some threads that indicate it can strike pretty much any time. I just booked an appointment to see my GP next week - I hope he can help or refer me somewhere else before I manage to completely destroy my relationship with my partner and my son.

How do you get over this hump? Can you learn to just turn off this new found side of yourself?
I hope there is hope.