Hello,
You've raised an important issue here that doesn't get talked about enough. It's more common than many people think.
It is a distressing sight to see a parent who is drinking more and more alcohol. It may often start as a way of coping with stress, maybe problems at work, relationships, or when an illness such as cancer is in the family. Your mum maybe doesn't see it as a problem, although she did admit to you it was getting worse, possibly a fact she doesnt remember telling you. Drinking more isn't her fault - it may have just become a habit which she cannot break out of...
It sounds like your mum and you are close, and you can say to her that seeing her drink makes you worry about her health and it's making you feel anxious.
I'm wondering if your dad and brother may have noticed too, but no-one is talking about it. Perhaps when you've got your dad on his own, you could say that you are worried about your mum's drinking. It feels a bit unfair of your mum to expect you to keep your worries to yourself. She may not be an alcoholic yet...if it's a recent problem...and often people who drink will deny strongly that it's an issue when asked about it.
If you feel you can't talk to anyone at home about it, (and I can understand it's not always easy), then perhaps you could have a word with the school or college counsellor, or someone else you can trust?
There's a helpful webpage article 'Coping with an alcoholic parent' (Teens Health, which is an American website) which may help you see you're not alone. There's also an organisation called 'Alateen' which has a website and meetings for teenagers between 12 - 17 who has a parent who is an alcoholic.
If you'd like to talk things through more privately, please do message us here at riprap, using the 'get in touch' form. You'll need to tick the box that gives consent to us emailing a reply...
Warm wishes
Sue - riprap