Advice please

Cynthia

So, I am 14 and my mom just had a baby. I never wanted a sibling because I didn’t want to have to take care of the baby all the time. My mom recently just had my sister. I love her so much and I always help out and I have no problem. My mom recently stop taking her to daycare because she had diaper rash multiple times. Now that I am in summer break I have to watch her every weekday and wake up at 5:00am and watch her 5:00-4:00 and my stepdad sleeps because he works nights and has to sleep during the day. I also don’t get paid because I need braces and that’s expensive but I still have to pay the down payment because my mom “can’t afford it” so I have to take $600 out of my college fund and I only have $800 in it. Since I have to watch my sister I can’t really see any of my friends besides the weekend and I can’t get a job because we don’t have a babysitter. I feel like this is so unfair but if I say something to her she says “ I pay for your soccer or She takes me to the store” but I feel like it’s so unfair because the baby has the whole basement filled with toys and I have to pay for my braces. Am I overreacting? What should I do? How should I talk to her without her yelling at me?