How do I get my mom to pay attention to me?

You said your mom goes tanning and running with your sister, and that's how they spend their time together, so how about finding a mutual interest you both enjoy. I don't know you or your mom so I don't know what you guys like, but there are a million things. Ask your mom to go bowling with you, that's always fun and you can even bring the rest of your family. Find something you love to do and stick with it. If your mother sees you following your dreams or showing a passion for something, she will support you, and- just in case you didn't know- support is a way of showing attention and the feeling of being worth something. Don't react to fast to the attention she's paying to your siblings, at this point in life they may need the attention in their own way. They are possibly feeling they way you are. But regardless, you have to live for yourself. You can't always count on someone being able to make you feel secure in yourself, it helps, but it's not a necessity. Once you don't need approval you will be able to accept it when it is shown to you. Hope I helped.

First, calmly approach your mom and state your feelings. If she continues to ignore you, set the house on fire and claim a leprechaun told you to do so. She's guaranteed to pay you attention then!

Tell her that your need her, too. Seriously.