katie I would definitely recommend you use a dummy. I know it might cause nipple confusion but you need a break. As long as you really focus on the latch you should be fine switching between them. I didn't persevere with a dummy with DD1 as I had very negative opinions of them, and I so wish I had - I had MONTHS of her snacking on and off all day and all night. It was terrible - exhausting, draining, depressing, miserable.
With DD2, she just has the dummy very occasionally when she is fed, clean nappy on and winded, but getting overtired and stressed. I try to take it out of her mouth just before she completely falls asleep.
Also - is she getting hind milk? Are there 'curds' in her poo? Lots and lots of foremilk can make the baby unsettled.
I so so feel for you. I think I may have another marathon sesh on my hands tonight as DD2 has done two huge naps - and I didn't get to nap because people were here . I am so stupid. I should have shooed them out the door and gone to bed!!!! IDIOT!!
katie can you get some help? You NEED to sleep - even for three or four hours in a row would help. (I know from my bl**dy sleep charts with DD1 that a block of three hours in a row is the minimum I need to feel vaguely sane.)
(Btw - I know your DH wants his sleep before "going back to work" but IMO looking after a baby is 24/7 work... tell me to bog off if you like but I feel very strongly about this!!)
I really hope you manage to get some help.