I was in your boat too MakeItUp-same except I was a few years older than you.
It is FUCKING HARD having a baby on your own. Can I say that again.
FUCKING HARD.
Got that? You need to stop beating yourself up.
None of my friends had had babies yet and they really didn't get it at all..
I did have PND, but went unmedicated because I thought I was just a rubbish mum, whereas in hindsight I was doing fine.
I kept ds warm and fed and cuddled him and walked up and down with him for hours when he was colicky-all by my self.
I also moved near my folks when he was a bit older than your dd, and had no mates.
No-one to have a coffee with, or go to the park with etc, which was worse in a way-I had my mum, but was really isolated.
I also found playgroup awful the first one I went to. All the other mums wore Gap jeans and had expensively blonde hair. I wore a leopard print mini skirt and a Metallica T Shirt...
They were real stepford wives who totally ignored me.
I was very lonely, but I went to college too, and then I found a fab playgroup, where I made friends! And It was much, much better.
No woman is an island. You need other people, you need fun, you need the occasional night out.
Persevere with trying to socialise at mum stuff. Not all playgroups are alike, and not everyone will judge you;
One of my friends I have made recently is a 25 year old mum of two-ostensibly we have nothing in common, but actually we get on great.
PM me anytime, if you need to offload, because I truly do understand.x