Not drinking enough or I don't have enough.

Maritza • Momma bear to two girls. | Az | Proud single momma.
Baby P will be wide eye and alert at the beginning of our nursing session. About 10-15 mins later she starts falling asleep and I don't hear gulping. I try to wake her up but she still sucks and is asleep. Like I'm a pacifier. I let her unlatch on her own time and I try to give her my boob again only for her to fight it or she lathes for a few minutes. I try to burp her, put her down and about 15-30 mins later she's up again nibbling on her hand.  Is it that I'm not making enough or she just falls asleep? Or she isn't getting enough? 
I can't be feeding her all day because well I have a 4 year old and in the process of finding a new job, plus cleaning the house and all those chores. I do give her formula as well.