Hi OP, well done! Have you been shown different holds for the baby? Laid back, football hold, lying on your side, etc. What works for one person doesn’t for another. Also, a specialist breastfeeding pillow can sometimes make the world of difference (not just a gimmick, promise!). If you haven’t been on there already, Kellymom.com is a very helpful website.
When you’re starting off, 4 days feels likes a lifetime. If you already have a good supply, that is amazing though.
If you feel able to persevere and you are happy with baby’s nappy output (lots of wees and 2 good poos a day at this stage, the NHS webste currently says - poos only space out later), I would be tempted to keep going as you are and freeze the milk.
However, if you have any concerns about your baby getting enough milk then please do not be scared to top up. My baby was combi-fed from quite early on as we weren’t getting the wees and poos in spite of a perfect latch and demand feeding. Still not really sure why but I never leaked milk and he never seemed to be swallowing a lot - some sort of low-level supply issue I think. I had a lot of trouble pumping so bottle fed a mix of expressed milk and formula. The breast milk definitely suited his tummy better - less wind and eased his constipation - so was worth the faff for me!
I know people say to top up using sippy cups etc to avoid nipple confusion. I remember the NCT breastfeeding lady telling us the baby would lap the milk. Well nearly all of us in the class tried it at some point and decided it was bollocks - baby didn’t take any bloody milk!