Like you, I started taking Domp. when my baby was 3 1/2 months old. And I learned that, just generally, it takes longer for Domp. to work the later you start it (counted from birth). Apparently, chances are if you start taking it in the first week or 2 it takes just a few days, while if you stat 3-4 months down the line you can expect it to take up to 6 weeks.
For us, there was an increase in milk supply by the second week, when DD refused 50 ml (ca 1.7 oz) of the extra (donated milk in SNS). 250 ml (ca 8.5 oz) was the most she ever took, just the first week of taking Domp. A week later she started to refuse another 50 ml ( we gave her 50 ml extra, offered at up to 6 times spread out over the day), then it kept going down by about 50 ml per week. About 2 1/2 months after starting the Domp. we used the SNS for the very last time, in the last couple of weeks we'd offered her some extra only if she seemed hungry, maybe every 2-3 days or so. By the next weigh-in, 6 weeks later, she had gained better than ever before! And we've never worried about her weight since then, she was below the 3rd percentile and investigated for FTT at 3 1/2 months. I kept taking Domp., but think I started to, very slowly, cut down on it, and had stopped taking it by the the time she was 12 months old (could have stopped around 8-10 months, maybe?).
I don't even remember how much I took, but I know it was as per what Dr Newman recommends at his website.
And what Megan says about milk removal is what I was told by our specialist ped too. He recommended that we cut down the feeds (when it seemed like DD wasn't wanting them, so when she refused a lot of a feed's extra for a day or two, we'd just stop offering that, and keep offering the breast a lot), to make sure she removed all the milk possible. I don't respond well to the pump, so that was never an option for me.
