I am four months pregnant and I was wondering if I could take musonex? They said that I could risk thinning my mucous plug and losing my baby.

Sure - go ahead. Based on the limited data, an increased risk of adverse birth outcomes has not been observed following maternal use of Guaifenesin in pregnancy. Alcohol may be present in some liquid formulations of guaifenesin. If consumed in sufficient quantities during pregnancy, fetal alcohol syndrome may result. Guaifenesin has been investigated as an agent to improve cervical mucus and improve fertility.
Would not take Mcx. Avoid medications during pregnancy unless absolutely necessary and approved by your obstetrician.