Struggling with sleep and mental health

I will preface this long post by saying I'm not sure if I'm looking for advice or just needed to let this out but LO is 7 weeks now and my mental health is deteriorating.

Husband and I take 7 hour shifts for the night (mainly because he needs at least 7 hours to function during the day). He does 8pm-3am and I do 3am-10am. I EBF so he will just wake me up for about 20 mins when the baby needs to be fed for his shift, which is at least every 4 hours because she doesn't sleep through the night.

She has very bad gas and reflux and for the past 2 weeks have refused to sleep in the bassinet or anywhere on her back (including cosleeping in bed). Within a couple minutes, she will start grunting, straining, then spit up and full on scream crying and if I don't pick her within seconds, she'll wake up and it will be near impossible to put her back down to sleep. We have tried everything including gas drops and probiotics. She will only sleep on us chest-to-chest upright for all naps and night time sleep. So we are basically nap trapped because she won't even tolerate a wrap or carrier.

My husband manages fine during his shift but I do not which makes me feel inadequate already as a mom. During my shift at night, I try my best to stay awake but will start to doze off and I am scared of dropping her while she sleeps on my chest so will put her down in her bassinet to pee, stretch and just wake myself up. But this gives me so much anxiety to just do this because she feels like a ticking time bomb and I don't know if she'll start screaming in 30 seconds or 5 minutes. It's to the point when she start crying I immediately start panicking and sometimes just cry with her while I settle her back on my chest until her next night feed.

During the day once I feed her, she'll fall asleep on my chest and I'm stuck there for at least the next 2 hours until she wakes up for the next feed. I'm already so exhausted that I can't even get myself to try and keep her awake to do any tummy time because I know she'll just spit up and cry and I feel guilty that she isn't getting proper developmental activities during the day. For now my husband and I take turns for day time naps but he is going back to work in a week and I'm not sure how I'm going to get through the day when I can't even get up to pee or eat. I just feel completely at a loss for what to do, what's to come, exhaustion, and every day just feeling like I can't do even a day more of this. Thanks for reading my long rambling.