How to Grow a Backbone

“How do I grow a backbone? I tend to say yes to everything and everyone. Then I get taken advantage of and angry at myself. It happens at work a lot, not [being] compensated for things that I'm spending money on or asked to do some extra jobs that cause extra work and to lose focus on my actual work… When I spoke up most recently, I got hostility, a long and loud argument about why it's impossible. That becomes scary, i HATE confrontation and disappointing people. I can't quit, I need to be heard and understood.”