Doesn’t want to eat

Ke

My LO is 20 weeks and EBF

we didn’t have problem with anything up until now, she doesn’t want to eat and if she does she eats for a little and then starts crying or has been gagging and it’s from both breast, I don’t know what’s going on but I dont want her to starve either and it’s frustrating that she doesn’t want to eat, any ideas or has it happened to any of you?