Poor you! I had a cold for almost the entirety of my second pregnancy, and it just stank, especially with another little one to take care of. You must have a very helpful 6 y.o. You could do what I did. Go see a homeopath, who can help you with a non-toxic remedy safe for pregnant moms and fetuses.
The drug sheet on Benadry (Diphenhydramine) reads as follows: has not been adequately evaluated in pregnant women. It should be used only if the benefit outweighs the potential but unknown risks. Tylenol has the risk of liver damage according to the official Tylenol web site and is not recommended for use in children under 12, which your baby is.
Sometimes you gotta do what you gotta do, but homeopathy is an option many people do not know about. If you live near a big city, you can probably find a professional homeopath in the phone book. Wishing you speedy recovery!