OP I could have written a very similar post to you when my now 3.5 year old was a baby.
I struggled on through 6 months of breastfeeding (we were actually doing combined feeding, but I was putting her on the breast first for every feed), despite it being excruciatingly painful each time. Despite being checked for latch, tongue-tie etc, somehow it never quite clicked. She never latched properly, and would doze off on each feed, so would take forever to get what seemed like a miniscule amount of my milk, then guzzle ounces of formula in seconds afterwards.
It turned out that she is massively hypermobile, and it is highly likely she just didn't have the strength in her jaw to achieve a good enough latch for bf. Nothing either of us could have done about that.
I''m not saying that will be the case for you, but I wanted to tell you about us as an eg, just in case there is something beyond your control that is in the mix here. Also, you will see on a lot of bf threads on here that it is relatively common to have persistent issues bfing one child, but to be fine with another one. Who knows why, but it happens.
Please don't beat yourself up, or resent your son for this. You are both trying your best. Bf is hard for a lot of mums and babies. I hope you eventually crack it together, but if you don't, your baby will also thrive on formula. It's hard when you are in the middle of it, and it has been drummed into you that bf is the be-all-and-end-all, but the vast majority of mothers will tell you, a little way down the line, that it really isn't. It's no reflection on either of you if it doesn't work perfectly. Many, many mothers and babies find it hard. If it becomes too hard, and you can't sort it, and is making you too miserable, formula is fine. One way or another it will work out.