16 weeks pregnant and getting over a bad cold, today started bad diarrhea- is this normal, and when should i worry ?

Diarrhea in pregnanc: Diarrhea is common at any time for many many reasons. One question is whether or not you had antibiotics during your cold and then the question of diarrhea become somewhat more important. If not then you can try home remedies or over-the-counter Imodium (loperamide) which is completely safe during pregnancy.

Viral illness: Hopefully you were not taking antibiotics and now have c. Diff colitis. If not, the diarrhea should ease up in the next 24-48 hrs. Stay hydrated, and if the diarrhea persists beyond this or you develop fever, or you received antibiotics, go and see a doctor. It is not likely this will be harmful to the fetus. Have a great baby and enjoy.