I am 23 weeks pregnant. Why am I losing so much colostrum?

By losing do you mean leaking? If so, this is a normal part of pregnancy. Your body is gearing up for the lactation process.

This is caused by the increase of a hormone called prolatcin that increases during the latter stages of pregnancy and continues until lactation begins on or about the 3rd to 5th postpartum day.

Yes, very normal. Some women experience it early on in pregnancy, and some don't experience it until baby is born. Everyone is different.