What am I to do?

Last night, I believe had a minor nervous breakdown. After my rehearsal for my show on Friday. I tried to call my sister again who has called me twice in the past two days. Which is odd because my sister NEVER calls me. The first time she called me, I asked her how she was doing and she said she was fine. I then asked if she was ok, and she told me yes. We stayed on the phone for about 5 minutes. Right after we hung up, I called her right back and asked if she was ok, and she told me yes again. I asked if she was sure. She said yes. Something did not seem right, but since she said everything was fine I let her be. She told me recently that I don't treat as if she was an adult. So I am trying to give her freedom. So last night she calls me again. As soon as I see the number I realize that something is up. I pick up the phone and my sister is crying. After many attempts of her telling me nothing is wrong she then tells me her girlfriend. And my sister tells me that she is crying in the staircase, but she would not tell me what exactly happened. Then I hear that her girlfriend came, my sister and her girlfriend start argueing. My sister is screaming "this is why I cut myself and I hope I die". The phone hangs up. I tried calling back like 10 times no answer. Then her phone is going straight to voicemail.
I call my brother who is in Brooklyn and I tell him to go to my sister if shes ok, and hes sick and cant get out the bed. He thinks he has pneumonia. My mother calls me and tells me she can't come here this weekend because my brother is sick and he can't watch my littler siblings. And she's crying because she's telling me she's broke and really stressed balancing everything.
I'm dealing with my classes, graduation is less then 4 months, I am scared for my sister, I can't help my mother...
I am falling apart. Last night I couldn't stop crying. I was alone in the apartment. I wasn't even strong enough to pick up the phone to talk to a friend. I cried myself to sleep. Everything around me is falling apart. And I can't stick anything back together. Then I woke up this morning, to go to my 10 30 class which I had an exam for.