Completely normal OP.
Sleep deprivation really is torture and can make you mentally unwell.
I remember crying inconsolably and regretting the whole thing, not the baby herself but the decision to change my life for what I felt was 'the worst'.
I was also the first in my friendship group to have a baby so that was a double whammy. Their lives continued all fun and carefree whilst I was sleep deprived, hormonal, fat and stuck to a crying baby 24/7.
My days! It was horrific in some ways.
My baby is now 3 and I have another who is 1. My pre baby days are kind of a distant memory now despite it being only 3 years. The same way school, university, previous jobs are. So i dont miss it like I did because I've been in this way of life for so long. You can still clearly remember the life before.
Now the trick to get through it that worked for me is:
You are in this now. You can't undo it. There is no going back. You can cry, you can regret, you can be bitter and miserable. But you'll still be in this situation. So therefore throw yourself fully into it 100%. Lean in to it, not back. This is it from now on. Don't hold onto any scrap or your old life. It's gone. Look back on it with rose tinted glasses or forget about it completely. But that chapter is forever closed.
Once you except that the pining and longing stops.
So now you throw yourself into this. Make the most out of what you have as it's all you have. Baby groups, walks, weaning, playing etc. Join everything and anything. Go for lunches with other mums, pilates with babies, swimming, cook weaning recipes etc.
Plan your evenings for the worst. Tell yourself your baby will be up every 2/3 hours. Give yourself no hope for anything else and plan for that.
Step fully into it, don't put 1 foot in and 1 foot out (hanging on to the old life).
As time goes on and you've fully got both feet in. You'll soon be in your 'new life'. The previous life will feel like a previous chapter of many. Then suddenly little bits of freedom come back. A full nights sleep. A full evening on the sofa watching a movie whilst baby is in bed. Then the odd night out etc. You slowly go from being 100% 'on' to 90% then 80% then 70% etc.
But you'll get there faster if you lean into it faster.
Changing my mentality was the only way I got through. Then when I was fully into it, I got pregnant again and the second slotted in before I was 'fully in it'.
You will be fine, I promise you this. It just takes time x