5 week old chick gasping !!!?!!!

I have a 5 week old FBCM. She started off with issues pooing. Had a prolapsed vent and an excoriated bottom. Poo was very wartery. Treated bottom with warm rinses and a series of salves. With treatments she'd spit up some clear mucus. Started sulmet in water and diflucan by mouth. Butt began to heal and but poo still wartery. Yesterday she started the gasping/gagging motion noted in the video. So I started her on IM Tylan thinking it's respiratory infection. She's isolated and no other chicks sho signs or symptoms. She gets medicated chick starter and has never seen the ground. Any thoughts ? Crop currently empty. She's not eating or drinking. I'm tube feeding nutri drench every 6-8 hours. Thought and comments greatly appreciated. Stopped sulmet as today was day 5 and started an antibiotic for CRD. Thanks in advance.

 

Video won't upload. It's a stretching of the neck motion and an opening of the mouth at peak stretch. Including pic of most recent poo