Are you expressing from the nipple or from behind? Watch a few YouTube videos but also the amount of colostrum you produce now doesn't indicate what your milk supply will be like
Impossible for big boobs! I’m the same; I’m going to wait a week before my section and pump
Have you tried a warm shower or bath before hand and a little massage. Also try not to get stressed over it, you need to be relaxed for it to become easier x