pressure on breasts

Monica

when I feeding her aftee like 5 minutes while shes sucking I feel this pressure almost pain feeling in the boob that's free. like something hard runs down from the top all the way to my nipple. sometimes I feel it on both of my books at the same time but mostly when I'm breastfeeding it happens to the one that she's not feedinh from. I'm not sure if I'm making sense...what can it be??