Massive, massive hugs, OP.
Reading all your posts (plus everyone else's) has reminded me of just how fucking shit life was for about 6 months with DS.
I fucking hated other mums.
Hated how they looked happy and wore clothes that looked clean.
That they could carry smallish changing bags around.
That their child gurgled and cooed and all that shit.
Mine puked. Projectile vomited ALL THE FUCKING TIME.
He screamed. He looked quite often like his head was going to explode.
Poor lad had/has CMPA/ various other allergies/severe reflux/severe colic/gastro issues and was generally just not made for this world.
He puked and shat like liquid bombs had gone off inside him.
One day I ran up the stairs to my husband's girly screams to find DS projectile puking/shitting and pissing all over OH, the bedroom walls and floors and anything else within firing range. It was hugely fucking grim.
I could never go out without about four changing backs worth of stuff that included enough muslins for all the babies of the world and several changes of clothes for him and me. Just leaving the house was an epic battle.
When I got to baby groups I felt like stabbing all those perfectly preened mum's in the eyes!
But - it got better! After months of him only sleeping upright on my chest (and me being so sleep deprived that I made a chilli with coffee from the percolator and put countless random items in the fridge, including my hairbrush, my phone and shampoo) he started to get better.
Ranitidine/Omprezole and Neocate saved us and we weaned slightly early and used Carobel to help thicken things.
After he was weaned, my life totally changed. I had allergies to deal with but there was just SO much less sick and he was much happier.
You'll be ok, I promise. Just take one day at a time and gather around a group of friends who can help you. Do you have something like a Homestart charity so you can get a volunteer mother's help in to support you? It'd be fucking brilliant if you can xx