The backstory would fill about 14 volumes, so apologies if I drip feed a bit but there is simply no way I can get all the information into one post. The problem essentially boils down to the following:
My mother is lonely, bored, depressed and miserable. Her cure for the above is to want to see me and DS as often as humanly possible. She lives a 45 minute drive away, we see her usually at least once a week but sometimes it might go a fortnight if we're particularly busy. I wouldn't mind seeing her more than this but she is relentlessly negative about EVERYTHING. If she's had a meal with friends/ gone on holiday/ been shopping and you ask how it was all you get is a litany of complaints. She is clinically depressed, and acknowledges this, but refuses to take antidepressants as she'd rather be 'authentically herself' (this is a dig at me as I take anti-depressants after suffering PND with DS). She also constantly wants to take over with DS and when I occasionally say things like 'please don't put the TV on now, he's going to bed in half an hour' or 'could you save that chocolate bar for after he's had lunch' she throws massive strips, cries etc. She can also be quite nasty to me personally, when she's in a bad mood, to the point I used to self harm because of how she made me feel. On the other side she can also be amazing company, and very kind when she wants to be. I try to be as understanding as I can but essentially I can't relax around her, and feel like nothing I do can ever be enough to actually make her happy, so have withdrawn a lot over the last few years in order to maintain my sanity.
I used to phone her every day because of horrendous guilt trips if I didn't, but once I had DS and simply couldn't afford to spend an hour or more on the phone each evening, I spent ages trying to cut the calls short and finally settled for calling about every 3 days instead. DS is nearly 3 and the guilt trips about this have only just (mostly) stopped.
Now I'm expecting DC2 in July and am on maternity leave, and she literally won't leave me alone. We have just got back from a four day beach trip with her and MIL, where she behaved horrendously, sulking every time she didn't get her own way, moaning constantly about the hotel, one-upping MIL and deliberately rubbing her nose in the fact that she's not as 'posh' or educated as DM. It's been excruciatingly embarrassing, and I'm fuming tbh, as is DH, and therefore apart from a quick text last night to say we were home ok (after she'd called DH and I three times each) I have been blanking her texts (for a whole 24 hours 
) as I just wanted some headspace to decide whether to try to tackle her about her behaviour or just do my usual tactic of creating space until I can cope again.
DH is working today and I was up a lot of the night with DS, so I asked FIL if he'd mind coming and taking him out for an hour to let me either sleep or do some housework depending on energy levels, and just as he was getting DS sorted to go, my mother turned up, as apparently she was 'worried' about me. She has a convenient theory that pregnant women shouldn't be alone at all after about 7 months, and therefore she should be round every bloody day while DH is at work. I looked less than thrilled to see her, and said FIL was about to take DS so I could sleep. I also said please could she not come round without at least texting first (have asked this before - don't generally mind random callers but I need to be psyched up to deal with her) and she got all teary and has gone off in a huff, saying I'm 'unnatural' for wanting to be on my own and for asking FIL (lives ten mins away, hasn't seen DS for a fortnight, happy to take him to park on his own) to help with DS instead of her (45 mins away, been with DS most of this week, just wants to talk at me).
She's going to drive me insane if she keeps this up but there is literally no way to get through to her without being horrible. She doesn't pick up on or chooses to ignore things like 'I've got a lot to get on with today' that most people would take as 'please don't come over.'
I also feel like I should try again to get her to go to the doctor about her mental health -even MIL who doesn't know her that well came and talked to me about it after spending two days in her company. But she doesn't listen to me about anything, and I just feel at the end of my tether and it sounds terrible but am actually ceasing to care 
. Her parents died ten years ago and then my father buggered off, so it's not like she hasn't had shit to deal with, but she's never made an effort to seek help in any way. I am her coping strategy and her emotional punchbag, and I'm fucking sick of it. I'm exhausted and can't believe I've got to spend what was meant to be a lovely restful few weeks of maternity leave, spending time with DS and DH and getting ready for the baby, attempting to erect and maintain barriers to stop her making everything bloody miserable. It's just exhausting and I don't know what to do. Everyone else thinks she's bloody wonderful and I'm an evil daughter for not seeing her more- she makes it sound like I ignore her for months at a time. On holiday MIL had a word with DH saying we should make an effort to see DM more as she's feeling lonely and cut out of our lives, and DH had to tell her we see DM about twice as much as we see her! She couldn't believe it as apparently DM had been making it sound like she goes weeks and weeks with no contact 
.