Why does manual pumping hurt

Maryam • first time momma

hello

i want to start collecting colostrum and im pregnant with my first

im using the medela hand pump it comes with the 24mm flange size

i tried pumping but literally the first pump it hurt rly badly and turned my nipple a little red and was sore to the touch for a few hours

help what can i do or what should i do and how should i pump to collect colostrum…???