Cold sores

So I started getting a cold sore on my lip this morning and wanted to try and get ahead of it getting bad so I took one one of my acyclovir pills because it's Sunday and the doctor office is closed. So then a little later I start wondering if that is even safe during pregnancy and now I'm freaking out (and defintely not taking anymore until I talk to my doctor) because it's not real clear if it's safe or not. I feel completely awful but I'm hoping just the one pill will not hurt my sweet baby. Anyone know anything on this that would be helpful?