Oh dear god I see this thread has descended into a BF vs FF bunfight. It always does 
Feeding is such an emotive subject. Speaking as someone who used to work in HV long before I had DD (so had no axe to grind re: my own feeding experiences at the time) I saw a lot of women who desperately wanted to BF but weren't able to for various reasons and the amount of guilt they carried around was overwhelming at times and contributed directly to PND in many cases. That is why I would always encourage someone who wants to BF to keep going for as long as they can - because often it's a case of a small amount of tweaking to get things to 'click' and then they will be glad they keep going.
OP I posted a similar thread around 5-6 weeks when my DD was feeding 24/7 as I was considering adding in some formula because I just couldn't cope. I was getting 1-2 hours sleep a night! She was making me so sore!
That's why I said to get silent reflux and allergies and posterior TT ruled out as all of these things contribute to constant feeding.
Newborn babies will nurse ALOT - for hours on end, that is normal. The reason I suggested Kellymom and looking at Dr MCKennas research into infant sleep is that I feel western parents often have unrealistic expectations about how much newborns feed and how often they wake up. It doesn't help that FF has been the predominant feeding method for decades in the Uk now, so people's experiences and expectations are often based around FF babies behaviour, not h normal behaviour of BF infants.
BF is definitely front-loaded in terms of effort. The first 3 months are awful... you can basically expect to do little else apart from feeding and expect your baby to wake frequently throughout the night. BUT once you get over the hump it just sort of clicks and you realize how convenient and easy BF is its sooo worth it in the long run (IME).
However, constant 24/7 feeding is usually not normal and can be indicative of something else going on (reflux, allergies, TT) so I think it's worth getting a referral to a lactation consultant and maybe seeing your GP to rule out reflux.
OP I really sympathize. I'd gone on BF training, taught other women how to BF, felt I had a pretty good understanding of how hard it was going to be at first so I felt realistically prepared and certainly didn't have rose tinted specs at how blissful and wonderful it was all going to be.... I was still floored at how hard it was at the beginning.
I kept going because it was incredibly important to me to BF my baby. I know it would have been detrimental to my mental state if I had stopped. HOWEVER there are clearly lots of time and when the opposite is true and if you feel that introducing the odd bottle of FF here and there is going to make a difference to your coping ability and preserves your BF overall then that is no bad thing.
With regards to the BF vs FF bunfight, the scientific evidence is pretty clear that human breastmilk is superior than formula milk. And that is not to say that formula milk is bad for babies (!!). Saying breastmilk is superior doesn't mean that formula isn't the next best alternative and thank goodness for the invention of forumla! Where in the past such babies would have been failure to thrive or worse.
(For example: www.who.int/mediacentre/factsheets/fs342/en/)
BUT there is also a lot of evidence to suggest that PND negatively impacts on infan development - so it is important to take the mothers mental health into account in these situations.
OP whatever you decide to do, someone will have an opinion and judge you negatively. That's parenting I'm afraid. You have to do what is right for your family and no one else can make that decision except you. So please don't let this thread make you feel bad either way. I would also respectfully disagree with the poster who said the fact that your baby feeds so much is evidence that your milk is not enough. If the baby is gaining weight well and has plenty of wet and dirty nappies then they are getting enough.
Good luck OP whatever you decide