Not meant to be a mom

This is long and incredibly hard to post, but I honestly hate being a mom some days. Like not just "today was hard" but I genuinely do not want to do it anymore. My mental health sucks no matter what medications I take, what doctor I see, or what I do. I love my kids and they do make me happy but I would be 10 times happier (as would they) if I only had to take care of them when I was good mentally and that is pretty rare. I get stressed so easily that I can't handle doing fun things with them. I go through long bouts of depression often that leave them getting the bare minimum. I loose my cool over tiny things and hurt their feelings constantly. I feel like a shit mom 99% of the time and I know they deserve so much better but no matter how hard I try I can not be that. Every special occasion, every holiday, every single plan that gets made, is completely ruined because I'm either stressed out and in a bad mood the entire time or I end up canceling because I can't handle it. With Christmas being in 2 days I'm feeling this extra hard because I can't do anything to celebrate with them and my husband only comes home 2 days a week, even during the holidays, so I have absolutely no help. I'm pregnant with #4 right now which makes me feel even worse because another child doesn't deserve to be brought into this. I grew up with a mother very similar to myself and I have no good memories of my childhood. It was very lonely and traumatizing. I've thought so many times that I should leave and sign custody over to my husband but obviously I've never gone through with it. Today I'm feeling it more than ever though. I think they would be so much happier getting to make memories with me during visitations than being miserable with me full time. I honestly was just not meant to be a mom. I'm not cut out for it. I feel incredibly selfish for sticking around and ruining everything for my kids.