Can a sinus infection that goes away on its own in a a week or two cause meningitis in fetus while pregnant?

Relax. Simple upper airway infections you have in sinuses/ears or even your lungs tend to be self contained. Meaning the germs do not enter your bloodstream which would be the only way they reach the fetus. A fetus might develop meningitis in the womb if your water breaks & germs enter the hole from below. This can happen but is rare & one reason they monitor labor so closely.