I really really, really really feel you (can you tell I had an awful time on mat leave!).
It does get easier.
I had to try several toddler groups/ activities before I found 'my tribe'. I then met up with them lots outside of the groups.
I made sure I had one activity/ group/ meet up/ errand per day so I HAD to leave the house and I got some level of social interaction. It broke the day up and made me not feel so lonely.
I then went back to work, and I realised quite how hard I'd been finding it, and eventually had to admit that I'd had some pnd - lack of motivation, feeling really down, finding 'easy' tasks daunting and hard, not enjoying my baby.
The PND naturally subsided as I got in to the routine of work, the increased social activity and the lack of being a SAHM.
SAHM is not for me. I couldn't do it, at all, in any way for any reason.
And I won't be having any more children.
However, I do now enjoy most of the time spent with DS. He is 22 months, he's got a bit of personality and I get respite from him! His sleep is still appalling though (4am was out start today) and the exhaustion doesn't help my enjoyment of him.
I also got dreadful nursing aversion, but because he was a bottle refuser I had no choice but to feed. I ended up resenting him a lot. That has now passed though.
I'd very much advise getting out more - the more you do it the easier it is.
And don't be afraid to leave him in the car when you get petrol!