Childish Attitude (Venting)

(Sorry if this isn't the right group, not really sure where it belongs. Just need to vent a little.)

I'm 22 going on 23. I'm currently living with family because my husband and I can't afford our own place on only his income. Ever since my nephew was born I've been a babysitter and provider for him. My sister has never offered to pay me and pretty much expects me to watch him whenever she needs. My husband and I never decline because hes really easy to watch and we love him to death, seeing how I've practically raised him since 3 months old. I've been looking for a job and recently applied where my future sister in law is working. I made the decision not to tell anyone until after the drug test and back round check (at most 3 days after interview), Until I got the dates and time to start my orientation. My brother walked in when I was doing my phone interview so he found out I got the job and he told my mom. My mom is now ignoring me because I didn't tell her the second i found out. When i did talk to her she was mad because i wanted to wait to say anything but since I'm my nephews babysitter I should've told her because now they have to make arrangements for his care.

Side note: My sister (nephews mom) is currently unemployed and I still have my nephew most of the time. She can go weeks while working without seeing or talking to her son. This past week she wanted to sleep all day and not watch him so my mom sent him home with me and he's been with me and my brother for 5 days until last night. Now he's not even allowed to come into my room to show me his new haircut. This also isn't the first time they've taken him out of someone's life just because they were mad.