Breast shield and feeding advice

Our LO is 2 months old, and it’s been a very long feeding journey. Had difficulty latching from day one. One week in with no midwife/hv support I bought a pump as baby was clearly hungry and not getting enough milk. We had a week of expressed milk topped up with formula (formula went straight through him). Until we ended up exclusively expressed feeding. It took us 7 different bottles to find some he could work with. At 5 weeks the HV suggested he could have a tongue tie and referred to the infant feeding team and for it to be cut. The HV also suggested nipple shields, willing to give anything a go to make our journey easier I purchased some and he instantly latched. Showing a preference for breastfeeding I slowly reduced pumping (oversupply), and have now been exclusively breastfeeding with the shields. LO tongue tie was cut just over a week ago. Still using the shields as he still can’t latch without them. I do have flat nipples so don’t know if this is also an issue. Now I’m concerned he’s not getting enough milk? My oversupply has definitely dropped. He usually seems quite content but he refuses to sleep in the late evening. (Got him down at 00:30). When he finally goes to sleep he will either wake every 3 hours or he will have a solid chunk of 5-6 hours before waking. During the day he will nap for 1-2 hours after his wake window and wake up hungry for his feed. I know your meant to look out for early hunger signs but I feel like he doesn’t get chance to have them. He wakes up crying hungry. Should I be waking him up sooner to feed? But if he has a shorter nap he’s overtired and grumpy. Not sure if this post even makes sense or what I’m asking for but just struggling with making sure LO is ok. I would rather not use the shields as it makes a mess (he pulls them off mid feed) but not sure how to improve his latch. He doesn’t lean his head back properly or open his mouth super wide. I don’t really want to go back to pumping and bottle feeding, controversial but I found this so much harder than breastfeeding. I know I could give up and formula feed but I really don’t want to. Especially after seeing how he reacted to it initially. He’s always been small for his age, he was born 10 days early, weighed 6lbs and lost 1lb in that first week. Back to birth weight by end of week 2, and slowly putting on weight. Now just over 9lb at 2 months. He’s getting weighted again on Monday to check he’s gaining weight.