Thanks so much for the hugs, mylittlepuds and tabbycat15. 
Compared to having a terminal disease, I feel my problems are insignificant. I know Mum will be really upset if she finds out how I feel, but I don't want her to worry that she's 'adding' to my problems by being ill, and thereby feel guilty about it. She's still alive so I just have to enjoy her while she's still here.
I know I'm peri-menopausal as I've had tests etc and haven't had a period for 18 months. I have all the usual symptoms! The last chat I had with my male GP involved him trying to chose HRT for me. Because Mum's cancer is a vigorous type, I've declined to have HRT and just try to deal with my symptoms naturally with exercise and diet. Oh, and I now see a lovely female GP for my woman's problems! 
To be honest, just putting everything down in this post has helped. I just felt really really down ? and alone ? that day. Felt like running away from everything and everyone. Also, I then read some of the other posts in this section and realised that, although I have a lot to deal with at the moment, I also have a lot of positive things in my life, such as my DP and son. My problems aren't as serious as other peoples'.
I'm trying to live by my mantra 'only worry about the things you can control', as well as the old 'one day at a time' rule.
Big hug to anyone feeling a bit down today. X