The cold shouldn't affect the embryo or fetus. And tylenol is considered safe for pregnancy. Though medications always may affect things in unknown ways.

As for confusion about the dating, you have run into the problem that the ob/gyn field has created.

The date of your pregnancy begins at last menstrual period. The age of the embryo/fetus itself is two weeks after that, at the actual time of conception.

The ob/gyn counts the two weeks prior as well, as some of the changes are an impact on your body.

So the age of the pregnancy is alwasy about two weeks more than gestational age.