Large nipples and breast. Hurting back and neck!

Rose

My babe is 3 weeks. Nursing ok but so far only snacking! I’d love for him to get fuller feeds. I have large breast and when I hold him up and sit up comfortably he always falls asleep so I have to hunch over to feed him and grab my breast and help express some milk while he nurses. This is killing my back. I’ve had painful flare ups. Any other advice. I’m so tired of this position and him eating every two hrs for 8-10 mins. Thanks!