5 week old fighting nursing all of a sudden

For the past two days she’s been acting like she’s hungry and she should be by her 2-1/2hr mark. She’ll latch for a few minutes then pop off and fight me to get her to latch back on. Her mouth will be open and almost frantic to find my breast but WILL NOT latch back on, and she cries. I feel bad cause I don’t know what to do.