While there is no evidence that your baby would be harmed if using Botox while still breastfeeding, you will likely not find a physician (at least an ethical one) willing to inject you. It's too much of a liability to provide a cosmetic (unnecessary) treatment at a time when you are still breastfeeding. Wait a couple months just to be safe.
Most doctors avoid administering Botox to pregnant or lactating patients. It might be safe, but it is difficult to design an ethical study that would investigate this question.
