I also only had 4 bumps that appeared and didn't have any others come up after they healed over. The Valtrex, from my basic understanding, keeps the virus from allowing it to replicate more or less. It is also safe to take during pregnancy as doctors prescribe it for expectant mothers who have herpes before they have the baby to keep them from spreading the virus to the baby during delivery. So, you should have no worries!
You can look up specific information on Valtrex on how it works by looking up the manufacturer and they have how it works for herpes, shinges, etc. Hopefully your itching will ease up now that you are getting the Valtrex in you. Congrats and good luck with the baby!!