I recommend getting a copy of
Breastfeeding and the Fourth Trimester by Lucy Webber. It was a lifesaver for me in those early weeks.
Understanding how breastfeeding works, and getting ALL the support available saved my journey. Private tongue tie assessment and cut literally changed feeding from painful to painless overnight. I literally continually bugged people until they helped me.
Baby fussing on the breast isn't necessarily a sign they aren't full, they are doing exactly what they need to do to increase your supply.
My little one was on my boob literally 8 hours at a time some days those first few weeks, and then whenever baby was needing to up supply feeding went mad again.
I also agree with PP about expressing not being a measure of supply. I could never express more than 2-3ml of milk (literally drops!) with my hospital grade pump, yet I definitely have plenty of milk.
I also read that if any of those around you suggest it is okay to bottle feed the probability of stopping breastfeeding was significantly higher. I was determined to breastfeed so I told everyone to never tell me bottle feeding was okay (not that I think it is bad, but I just wanted to minimise the chance of me giving up especially during those early weeks). I had so much support both from family, my partner and I reached out to NHS, private, NCT baby latte group, etc. I went on a breastfeeding course before the baby was born.
The first few weeks were very hard, but they were worth it for the ongoing benefits, both baby and maternal health, as well as practically.
We are now 18 months and still feeding. Baby went to nursery at 8 months 4 days a week and it didn't affect our journey at all.