Which Job Should I Quit

Chloe • 22, Bisexual, Taken, Proud Cat Mom 😸💜 NOT TTC
I currently have two jobs, both of which are very physically taxing and leave me exhausted and in a tremendous amount of pain every night. I cannot keep up with working both jobs since I've been oversleeping due to my exhaustion, having to call in from literally not being able to walk, and having to deal with regular injuries due to over straining and overworking my body.
This second job (Job B) I have only been at for about a month. My other job (Job A) I've had for about a year and I'm close to my manager. So here is my dilemma:
Job B is third shift(I don't get home until 1am), I am paid $11 an hour, Im guaranteed 7-8 hour shifts, work Monday-Friday, and am paid weekly. 
Job A is first shift (I have to be up by 4am) I am paid minimum wage: 8.50, and I only get ~4 hour shifts, two/three days a week, and a paycheck every two weeks. 
So obviously Job B is the better option. But I have loyalty to Job A and my manager really relies on me, and recently two people in my department quit which puts more pressure and expectations on me. But they keep cutting my hours yet they expect me to make them a priority since I worked their first, even though I make shit money and basically gave me the ultimatum that I have to quit my second, better paying job, or I'll be fired. 
PLEASE help me through this decision and give me any advice/insight you may have on this situation. I'm so stressed out 

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