Would it seem selfish of me if I put my niece and nephews in foster care?

My niece and nephews live with me...they're 3, 2, and 1 years old. This is very hard for me because I live in a studio apartment, I work full time, and I go to school full time. I get no help from my family and the stress is to an almost unbearable point. I have recently become severely depressed and everyday seems to be a struggle. I'm starting to think the best thing is for me to put them in fost care. I was raised in foster and I know how awful it can be, but I need a break, even if it is only for a couple of weeks. Would this be selfish of me? What should I do?