Gosh this sounds like my LO.
He was 50th percentile for height and 2nd for weight but didn't track the weight curve, kept dropping under the 2nd line. I had him on my lap, lying on a cushion on the boob, for about 20 hours a day at 6 weeks.
From about 4pm till about 11pm it was literally none stop. DH would come in, cook dinner, and I would eat it, plate on the arm of the sofa, fork in hand, while bub was still on boob. And flipping expressing to try and increase my supply, so even when baby was off I was still doing it, and had bottles to sterilise to put the milk in etc, it was endless. I found it so difficult. Easily the hardest thing I have ever done. You are doing so, so well. 
If you give up now, you have still given your LO a wonderful start, and being a happy and healthy mummy is much more important long term than anything else. On the other hand, if you just aren't ready to stop now, there are ways of maybe getting a bit more help. A BFeeding clinic is a really good idea if you can possibly get there.
There may be several solutions, but if it helps, what the lactation midwife suggested to me, was that the length of the cluster feeding was excessive, even by cluster feeding standards at that age, and, together with the disparity between height and weight, it suggested that DS needed a little bit more milk than I was producing.
She told me to try introducing one small feed a day of supplement to help him at the time he was most restless and hungry. She suggested at 6 weeks it would not cause nipple confusion or upset the Bfeeding, but might help me continue to for longer. She suggested that I buy those little bottles of Aptimil that come ready sterilised (NOT the powdered formula that you have to sterilise etc) and to give the baby 100mls a day. This meant I had sterilised bottles and teats, and opened the formula and poured it in. It is a bit more expensive than the powder but much easier than faffing about with it all.
This made an immediate, massive difference to mine LO. He was just a different baby. Still fed a lot, but without the desperation, IFSWIM, feeding in a manageable way I could cope with.
I would never have done this without the specific advice of that midwife, I was terrified of nipple confusion, giving up, obsessing over how much to supplement etc. It was really helpful just to be told what I needed to do and do it, if that makes sense!
(My LO never caught up his weight until hitting 6months and solid food, at which point he burst through the percentiles until he was at 50th centile for both weight and height, where he has stayed ever since. He is now nearly 2 and still on the boob, when he wakes up and when he goes to bed, and they are now the happiest bits of my day.