Oh love, that's so hard… I've been where you are before Covid (PND, epic non-sleeping baby, exhaustion) and it was terrible. And I was fortunate enough to have a HV and a good group of other first time mums. It was still monumentally hard - so must be even harder for you.
First thing - give yourself a huge big-up for managing so well without support, and looking after your baby so brilliantly. (I know you don't think you are, but I see someone who is cuddling, feeding, putting her baby first… ok?) Huge credit too for recognising your PND and getting help. That's really brave. You're a fucking warrior, ok?
Second thing, recognise that this is really hard, and it's perfectly normal to reach the end of your tether from time to time. You're not weird or wrong for losing it. The important thing is what you do when you feel you're on the brink of losing it. And you 100% did the right thing. You o
put your baby somewhere safe and took yourself out of the room to let out your stress and frustration. Big tick in the good mother box, right there, ok?
(Side note - that's what it is - stress and frustration. I know it feels like anger, but anger is something we easily blame ourselves for, stress and frustration is an understandable and proportionate reaction to a stressful and frustrating situation. It night help to give yourself a break if you identify your feelings this way. You're not angry with your baby. You're frustrated and stressed out by his inability to go to sleep and the screaming that comes with it. That's a normal reaction and has less guilt attached.)
And while yes, they do pick up on stress, and it probably doesn't help him to fall asleep, I haven't seen or read anything which suggests it does them lasting harm. You've probably not helped your immediate problem, but you haven't created lasting ones for your little boy.
I got to this point several times with my first - who never fucking slept: couldn't fall asleep, couldn't stay asleep, never took a nap longer than 20 minutes. I had PND too, and blamed myself for everything, and convinced myself that I was harming her irrevocably by getting frustrated and by my inability to 'fix' her sleep - which was definitely, in my mind, caused by something I was getting wrong.
She's now 13, perfectly well adjusted, securely bonded with me and flying high.
Still not much of a sleeper though... just how she's built.
In terms of practical solutions – do you have any friends with similar aged babies that you could feasibly bubble with while you wait for Covid restrictions ease up? Or even just arrange to meet up a few times a week outdoors to vent and chat and share problems with? Because the isolation you're experiencing will be making this all much harder...
And second the posters above who suggest getting hold of your HV and pressing hard for a visit. She'll check your baby and reassure you if nothing else, and that's hugely important.
Also, please try and make sure you're eating properly, and enough... you don't need to be running on empty physically too. x
Meanwhile, have a virtual hug. xx