IrishMaeve
I'd really recommend you start a new thread, just so your post doesn't get lost in the discussion.
Having said that - do you want to continue breastfeeding exclusively? There are many people here who are excellent at giving advice and support, something that seems to be sadly lacking in real life unless you go hunting for it. You may want to try contacting a BF counsellor:
La Leche League or the NCT have helplines with BF counsellors.
6 weeks is notorious for a big growth spurt, where the baby seems to feed and feed and feed...the best advice I can give really is to let him.
I would also say not to worry about the 'amount' he is getting - if he is coming off the breast himself happy, then that's a good sign.
WRT not putting on weight - is he actually losing weight? Or slipping slightly down the centiles. It unfortunately seems to be very common for HVs to worry new mothers about how much weight their DCs are or aren't putting on (mine suggested not feeding on demand when DS started zooming up the centiles as a newborn, and then putting him on formula once his growth slowed down...I ignored her both times). Is he alert, happy, hitting any developemental milestones? It may be that there is no problem and he's just putting on weight at his own rate. Without knowing exactly how his weight gain is going though, I don't want to mislead you, but from what you have said in your post, there doesn't seem to be a big problem.
If you choose to switch to formula because you decide it is best for you, there is nothing wrong with that - you've done an amazing job exclusively breastfeeding your son for 6 weeks, and you should be proud of that. But be sure it's what you want to do, and that you don't feel pressured into it by a HV who want s your son to hit a line on a chart.