foxy my lovely for you, but try not to feel too upset about it; 2g is less than a tenth of an ounce and I think your HV is being less than supportive if she is making you feel bad about that. derlor mentioned last week as well that a poo can weigh half an ounce. Is she getting longer? she may be too busy being long and skinny rather than short and fat. I breed the short and fat variety myself.
Talk to your GP, talk to the NCT, see a lactation consultant, but don't feel undermined at a 2g weight loss. the mantra on here seems to be if she is happy and healthy and weeing and pooing, then she is fine, and that weekly weigh ins are counter productive as their weight can vary enormously. I hope you're feelin OK though, and not beating yourself up about it.