Cold sore

Anyone else experience a cold sore while pregnant. I am currently a little over 12 weeks and woke up a couple days ago with a bad one... I called my OB and she perscribed valtrex and also said I could use abreva (both category B). But, I am still really nervous about using them. I know my OB wouldn't prescribe me anything that would harm my baby... But I am still scared! Anyone gone through this??