Taken advantage of

I've been working at the same place for 3 1/2 months, starting wage was at $8. After you've been there 90 days you get a raise based on how you've been doing. All I got was a 25¢ bonus (was expecting a dollar since minimum wage is $9), compared to everyone else I've asked I've earned the lowest raise. I'm also only 15, whereas they're 16 and can work with less restrictions, etc. Multiple times I've been told by customers how I'm better at my job than most of the employees there, and my managers always have me doing their jobs for them. It's ridiculous. Every time they've called me and asked if I can pick up a shift I've said yes. I've never ONCE said no, and my availability is whenever they need me. No questions asked. Whereas the other employees are completely opposite. I feel like they're discriminating against my age. An assistant manager pulled me aside and said he thinks my raise was bogus and I have every right to be upset. I work my butt off for a lousy $8.25 an hour. I'm assigned jobs that they're paying other people $15 an hour. I don't know what to do about this 😑