kiwibella, thanks for the update. Good for you and your dh to have spoken to the midwife.
Expressing - well, this will of course allow you to see your baby is taking milk, and this could be important if she is not transferring milk correctly. One of the reasons why we worry about lack of poo is that lack of poo can be a symptom of lack of milk in a newborn (not always - that's why it would be helpful to know how much your dd weighs, 'cos if she is an appropriate weight, we don't need to worry about intake).
The constant feeding could be a good thing - it might well mean your dd is making up for a lack of milk because of the unusually long sleeps, and we would worry more if she continued to sleep for a long time. So as long as she is transferring milk, then constant feeding is fine.
When constant feeding is not fine, is when the baby is never satisfied....because that could be a sign that milk is simply not being transferred effectively.
That's why if the bf support people are fully trained (ie breastfeeding counsellors and not peer supporters - who are great but who are not trained to do an assessment of a feed), they will be able to observe a feed and assess this for you.
There is nothing you can do with your own diet, by the way.
The vaseline will not help - the lack of poo is not because she is constipated in the usual sense; however when a baby is like this there is (very rarely) an underlying cause of her lack of poo, unrelated to milk transfer, and I feel after this time, this could be checked for, too.
Nevertheless, she may well do a huge poo any moment now, as a result of the improved frequency of feeds and improved milk transfer, and we will all cheer
If things are still the same tomorrow, though, then I do still feel weighing is in order.