I had all this with DS (now 2.3 and active, healthy and slim). It seems that history is going to repeat itself.
DD is 3 months and has reflux, which Gaviscon seems to be controlling She's a placid, happy, sweet baby - smiling, laughing, gurgling, and meeting all her gross motor milestones. But she's not gaining weight according to the HV's chart. Or indeed (for I checked this morning) according to the WHO breastfeeding charts. In fact, she's fallen out of the WHO one altogether (mostly because her weight gain from weeks 2 to 7 was terrible owing to the reflux (a mere 3 oz)).
To me, she appears to be thriving. And the HV only looks worried about her once the scales have been wielded. The HV will be back in 4 weeks - I am trying to up DD's feeds in the meantime and drink more fluids - and if DD still isn't gaining fast enough there'll be a referral to the GP, who will no doubt pass the buck to a paed, and I have no idea how to stop all this. Last time, I just stopped going to clinic but DS was 6 months by then, and this time the HVs actually make an appt with you at your own house so it's a bit tricky to just say 'I'm not coming anymore'. And I'm also concerned that they'll mark me down as a crappy mother (who makes crappy milk, obviously) and pester me even more. And I'm just pissed off with the whole thing. Aaargh.