what's happening?!!

My EBF 13wo daughter is starting to cry at one boob after a few minutes nursing at the bedtime feed. I give her the other side and she happily nurses and nods off eventually. Previously, we'd nurse for half an hour on the 1st side then 20mins on the 2nd side. I feel a bit run down at the moment and can't be sure if it's my supply? My boobs never feel full anymore and I feel less of a letdown - having experienced the last 12 weeks with a forceful and fast let down, I'm confused. Is my milk drying up? Is it regulating? Literally I feel so incredibly worried right now as after several persistent weeks of trying and several types of bottles I cannot for the life of me get her to accept a bottle so if I am beginning to get issues with low supply we're in real trouble 😢 please help