Scared, lonely and overwhelmed...

Had my 3rd child by c-section a week ago. Have two boys, 11 and 7, and I gave birth to a beautiful baby girl. I love her so much and I want to protect her and I'm terrified I won't be able to. I cry at night when no one can see because I'm overwhelmed and scared. I have no family nearby. The pain from the c-section and breastfeeding is really taking a toll on me.  I can't sleep when she is sleeping because I'm scared she'll stop breathing.. I don't think I would survive if something happened to her. Feel like I'm short and angry with my fiancé and my boys but I can't help it. Just so much on my mind. Fiancé helps as much as he can, but I'm the only one that can feed her and I try to not wake him up during the night because he needs to function at work. So I just lie awake and cry and wait for baby to wake up again... 
What do I do??  I feel so stupid. This is my third child, I should know how to handle this by now... Don't know what to do...