Should I get paid at least minimum wage for all the hours I work at my salary job?

I take care of a 10 year old autistic boy. I work from 9pm to 9am Sunday through Thursday night. I am payed a salary of $50 a day. That's 60 hours at $250 a week. Is it legal for the company to pay me this? Shouldn't i get at least minimum wage for the 40 hours and overtime for the other 20 hours?