Lamictal (lamotrigine) is also used as an anti-seizure drug; I know how to dose it for that, but not as a mood stabilizer since it's not used that way in veterinary medicine. In fact, it's so expensive that it's not used in veterinary medicine at all other than experimentally. Therefore, dosing is extrapolated from human medicine. I should shut up now, but I'll tell you my theory and in doing so, am trusting you to check with your doctor to find out THEIR theory since it's WAY way way way WAY way WAY WAY way more important than mine.
Lamictal has one very bad side effect present in the human population: It can cause severe bleeding problems in a very low percentage of adults. The first sign of these is a rash. Patients new to Lamictal are given slow incremental dose increases to insure that they are tolerating the drug and not going to bleed to death on it. (The first time you took it, your doctor probably warned you about the rash, yes?)
My theory is that since you already had a successful Lamictal trial, your doctor is confident that you will not develop a rash.
The reason I stayed up and wrote all this is two fold a) If I just came out and said the last sentence it would sound like medical advice and I wanted to be clear it was my rambling 3am theory, nothing more and b) If you are at all concerned, the side effects are serious enough that it would be totally reasonable to call your doctor ASAP before starting the drug. It might be that that's just the way this doctor prescribes this drug, but if you're concerned - it's your right as a patient to have the answer.
Hopefully these suggestions are not out of line. Anyway, goodnight.
~SK~