Oh ancelyn I'm so sorry to hear you're feeling down in the dumps at the moment
As mum said, it sounds like your SIL is just causing trouble for the sake of it so please try not to let it get to you too much. For now, just focus on you and the fact that you'll be getting some lovely squishy newborn snuggles soon!
Oh and wine and telly solves everything... Throw some chocolate and a nice hot bath in there and you've got yourself the perfect evening! 
If it's any consolation, it seems like everyone's having a bit of a rubbish time of it lately. A friend was supposed to come and visit today but no sign of her in the end.
My mum popped round as promised though, but after a quick chat, she proceeded to use my phone for half an hour (because she was out of credit and still refuses to get a contract - arghhh!) then moan about something in a way that made me feel like it was my fault before buggering off again.
On top of that I've just been feeling MASSIVELY fed up of being pregnant. Life has become so, so boring now that I'm spending every day doing the same thing and just waiting for this little one to arrive.
I just want to have fun things to do and interesting things to talk about again (as much as I love talking about baby stuff, I do miss having normal conversations once in a while!)
Sigh... Anyway, rant over. I realise I'm incredibly lucky to be pregnant and healthy and everything, but I just can't help feeling really fed up and like I'm being bloody boring!
Hopefully yoga tonight will help me to relax and stop me from being so mopey 