It is normal for colostrum to come and go during pregnancy. Some mothers dont see any until after birth (2-5 days when the milk matures). If you think its stress related try doing some mediation, breathing exercises, or even talk to your dr/caregiver about the stress issues. However, I wouldn't worry now unless your lacking milk when baby is born and your stressed.
Thank you I am just constantly getting told by my mother that stress caused her to lose her milk at 2 months postpartum and my husband always stresses me out so I was scared I wasn't going to be able to produce enough for my baby