Fussy 3 week old and I feel like I'm starting to lose it

My baby boy (second child) is 3.5 weeks old and I feel like I've been slowly coming off the rails. I thought I'd have more confidence and less anxiety as a second time mom, but my newest LO is just SO FUSSY and I find myself constantly second guessing everything. He has a bit of reflux and needs a lot of upright time after feeds so the cycle of feed/diaper change/upright time/sleep doesn't allow for much hands off or rest time. Even when holding him he is often grunty and unsettled. He generally refuses to sleep in his bassinet 95% of the time and the longest overnight stretch we've gotten from him is 1.5 hours and that has happened ONCE, so safe to say sleep deprivation is contributing. Absolutely refuses it during the daytime. We upgraded the bassinet mattress to a more cushiony version (still baby safe) and I've even tried co sleeping a couple times out of desperation and he just won't have any of it- he just wants to be held for all sleep. And honestly even being held he's not always content. My husband and I have been splitting the night into shifts so I can sleep from 10pm-3am and I pick up newborn care 3am onward. Husband watches our older toddler (2 yo) starting at around 8 or 9am when we dont have toddler childcare. My husband goes back to work in a week and I am FREAKING OUT because he won't be able to give me that overnight coverage for me to sleep anymore (he works 12 hr shifts in healthcare and needs to be well rested so he doesnt make deadly mistakes) and I don't know how I am going to survive without being able to put this baby to sleep in a bassinet!? Oh and also take care of a toddler who has been acting out since we brought baby home!?

Looking for advice, solidarity, anything really. Just feeling defeated and overwhelmed.