Slow weight gain - supply issue?

freezorburn

DS is 8 months this week and we just did a weight check today ... his weight gain has really slowed down. His curve looks like he has been gaining about 1/2 lb. per month going back to 4 months, and is dancing around the 2nd percentile line. From 0-4 months he bounced around from 15th percentile, to 3rd, back up to 25th, and now he has really tapered off to 2nd...

He is a pretty happy guy, doing a lot of rolling and pre-crawling and getting better at sitting without support. He is a beanpole, just doesn't have a lot of chubb.

Is it possible to have a low supply even though I seem to have a forceful letdown? DS will latch on, get the flow started, come off coughing and milk will spray everywhere, and then he will settle down and feed for a while. I tend to have more milk in the morning, I sometimes even feel engorged. I know he is still getting milk in the evening because I can feel it letdown.

We are offering him solids twice a day -- in the morning and at dinner, but I nurse him first. He doesn't eat a ton, so I guess that means he's pretty full on breastmilk. 

I've done the whole supply-boosting thing before, when he was 3-4 months... took fenugreek, pumped after feedings to stimulate milk production, then I tapered off both things when it seemed that we had things pretty well established. I wish I had weighed DS at 5 months but we moved to the UK and it took me a while to get him registered with a practice here. Wonder if I should try the fenugreek and pumping again, or is there something else going on with my supply? 

Would love to hear any ideas/wisdom that the board has to share! 

EDIT: he has only been gaining 1/2 lb. per month since he was 4 months old.