I sympathize with how you feel and with what you have been going through, are going through. Never apologize for writing "too much" about how you feel.
Remind yourself that what you have internalized is not normal or healthy -- that you should not expect to "monopolize" someone else's attention, that you should note expect to be heard and understood.
But this can also change. You won't be able to change your mom. But you can change the types of choices you make. You can decide not to "settle" for people that you know in your life who do not value you; who do not listen to you; who dismiss you; who use you for their own needs. You can raise the bar of what you will accept and you have the right to choose.
There may be people who drain you, who you should walk away from. It is ok to do that. It is ok to protect yourself; to see yourself as having value and as having currency with the world whether the people you have known have treated you that way or not.
The situation is not your fault. But there are things that you can do to change your scenario. Dare to matter, to yourself, and to expect to find other people to whom you will matter. There are such people out there in the world. Dare to seek out a whole other class of people.
Your mom may not be able -- or may not choose -- to change. It's ok to find other people to care for, and who will care for you. It does not make you callous or unfeeling. It just means you have finally accepted -- or are in the process of accepting -- that what you feel and what you want in life matters. That this does not make you selfish. No matter what anyone else might say.
I wish I could direct you to some websites or forums. The only ones I know of would be mentioned in my article, or as resources at the end of it. I think that, you are in a good place in some ways though, you are pretty young, and have your whole life ahead of you.
You are at an age where people often make big changes in their viewpoints, in their activities, in their friends, in where they live ... Embrace this knowledge and encourage yourself that you will be able to make choices that will be healthy and nurturing for you and that you will find others who will nurture and hear you as well.