hadit - this is one of the most ignorant, unhelpful and misleading bits of misinformation I have ever heard from a health visitor....honestly, wheeling out and shooting is too good for them. The very worst sort of HV is like this - thinks she knows it all, and ends up confusing people and possinly messing up their lives, and their breastfeeding.
It is preposterous to work out a volume of breastmilk especially when one of the participants in your lovely tandem setup is a toddler who could be eating any amount depending on what solids he has,whether he hurt himself and wanted a quick comfort suck, whether he's thirsty....etc etc etc.
She is clearly totally ignorant of the fact that a mother's metabolism is different when she is pg or breastfeeding, and it is crazy to work out the no. of calories in the milk (which you can only do very roughly anyway) and assume the mother needs to take in the equivalent in food. Not only is the metabolism different, but you have laid down extra fat in pg, which converts to energy to make the milk.
If you are having dizzy spells, it is possible you are going hungry or thirsty, I suppose, or because you are tired, or for many other reasons. You may need to eat a bit more for all I know, but not 2000 calories more a day. Does the woman have no common sense at all??
Now I am going to bed cross with your health visitor!!