baby cries at breast

So my daughter started nursing beautifully right after birth. Everything was going so well and then all of a sudden she started crying on my breast. She starts to suck and then unlatches and starts to cry bloody murder. You can see her get sort of angry in a way. She's fine for the first 2 minutes and then the crying starts! She is sucking a lot of milk I have a good supply but it's killing me ! I'm scared she's not eating enough i find myself crying with her because I can't feed her! I don't know what she wants and why she won't keep sucking. Any help or suggestions would be greatly appreciated.