Hey! So it could be Dysphoric Milk Ejection Reflex (D-MER). It's a reaction to the oxytocin involved in a let down. I have the same thing when pumping or breastfeeding...definitely uncomfortable and not favorable but not dangerous at all. You could also be dehydrated.
drinking something while breastfeeding used to help me a little sometimes but yeah I hatedddd that feeling and then eventually it just went away
This can be a very normal reaction. It could be hormonal changes and your body reacting to when you’re experiencing at letdown of milk where oxytocin is released. I exclusively pump and get the same feelings every time but it usually passes after a few minutes. Wishing you all the best!