Shar, it usually happens in most families, you grow up and it seems you have to compete with your siblings. Now your the oldest your mum may expect more from you.

She may think that, seeing as your growing up, you don't really want to spend time with her - but you do. You should try and mend the bond between you, try asking if she would like to come shopping with you or to the cinema or just have a chat.
She then can see what is really bugging you and begin to include you more.

I know what you mean about shouting and stuff. I shout at my dad a lot, butit doesn't help when my mum starts shouting at me too when it was completely my dads fault. She takes my side sometimes, but in others it's just like they are out to get you.

You shouldn't have to live in your brother's shadows, your mum should not favouritise any kid in their family. But you may also need to try and include her, so she will include you, if you get what I mean.