eandz, thanks for the further info.
This is a significant weight loss in just 2.5 weeks and I am confused as to why you seem to have been given no support or advice on this. Did the HV say nothing???
The percentiles can be hard to understand - they mean he used to be heavier than 97 babies out of every 100 and now he is heavier than only 47 babies out of every 100. But in fact, the concerning bit is the sudden weight loss. It can be normal, especially for large babies, to work their way down the centiles over a period of several weeks, without actually losing weight. What happens is they just gain weight a little more slowly and get to a lower percentile that way.
You're doing the right thing in feeding him at the first sign of rooting - and yes, offer both sides at least at every feed.
To be honest, though, I think your issue is beyond what can be addressed on a talkboard or by a bfc alone(I am an NCT bfc).
There is of course the possibility the weight has been recorded inaccurately - kg have been wrongly translated into lbs; scales are inaccurate; plotting on graph is inaccurate; baby was not weighed naked. All these I have seen, with mothers worried unnecessarily by these 'human errors'.
But if your baby has lost 1 pound in under three weeks, and you are confident this tells a true story, then I think you will be helped by speaking in more detail to the HV about what might be going on here. If all the situation is is lack of calories (and nothing else health-wise) then yes, he needs more calories .
Can you try this? First step would be to start expressing to get breastmilk to top him up with, after every feed (I would say). He needs to 'switch nurse' to boost his intake, and your supply, and to feed a lot at night - how does this sound? If you can, hold him close to you day and night so you can respond quickly to any sign he might feed.
But to be honest, it would be important to speak to someone in real life and get a thorough assessment of his health, growth and feeding. None of this means you have to use formula, but on the face of it, I do think you need to explore taking some action to address and explain the weight loss.