Famciclovir while breastfeeding.

So I got the start of a cold sore and I have a prescription for Famciclovir that is on file. I haven’t had one in a while and my regular pharmacy had a guy I hadn’t seen before. I asked about breastfeeding and he said it should be fine because I am leaving for the weekend and had planned to pump and dump till Monday so I don’t have to worry about sterilization and storage while away. So now I’ve been reading stupidly after I took the 3 500mg tabs one dose. And I’m of course freaking out that he should have just prescribed the other one that’s safer. Has anyone else out there taken this? What the heck do I do?