Need to vent

I'm 33 weeks pregnant and have been with my partner for 8 years but have only just moved in together into his house that his mum also lives in. It is his house though. My partner works away and so most of the time it's just me and her, after living here 7 weeks now it's all gotten to me. Shes a lovely women and means well but is not easy to live with, she undermines me with regards to my own dog giving her treats and letting her get away with things I try and stop her from doing and not only that her memories going and repeats herself often. We can have the same conversation 3 or 4 times in a night, which is mentally draining. She's also a bit of a hoarder and the house isn't up to my standard and however much I try to declutter and get things organised nothing in this house is mine, who am I to say what can be thrown out and what needs to be kept but shes never in to help as shes always running after my partners sister's. I've been so down and low this week that I've just been crying I don't know if I can cope with this stress as it's not good for the baby. I already feel bad for my partner as when he gets home tomorrow I'm going to offload this all onto him and I don't want it to be like I'm nagging him after he's been away for 2 weeks. His sister is single with a 2 bedroom house and honestly think she needs to move in with her and give us some space to become a family but who knows how that will go down. Sorry for the long post and thanks for sticking round if you made it this far just needed to get this out somewhere. I have spoken to my mum about it but not much as don't want her to worry about me.