Baby chicks very sick, choking/gagging, 15 dead already, please help!

[Chicharron]

Here is a video link so you can see what I mean: https://vimeo.com/1024119037?share=copy#t=0
So I posted a few days ago about suspected fowl pox in my baby chicks. Nearly all of them have scabs over their eyes and around their beaks. Yesterday I lost 3, found 3 more dead this morning. Despite the scabs on their faces, they eat, drink, and play up until a few hours before death. Then just stand still and a few hours later are dead.
Now I have several doing what the chick in the video shows. Stretching out their necks, mouth open, as if trying to swallow something stuck. This one makes a clicking noise every time it pulls out its neck. It has been doing this since last night. I felt around their crops and don't feel anything weird, except they seem pretty empty. Vents look fine, although some of them are pooping forest green poo.
They are kept in a brooder out in my coop on large pine shavings, brooder plate for heat, fed chick crumbles only. There's nothing else in the brooder they could choke on. I let them outside on the dirt for a few hours a day.
I have tried giving Nutri Drench and baby vitamins to the sick ones, no improvement, still dead within hours. I don't know what more I can do. There are no chicken vets around. Is this related to fowl pox? Something else? Please offer any suggestions, if I don't do something I think another 3 will be dead by tonight!

 

[Eggcessive]

Can you see any white to yellow material inside the chick’s beak, that might be wet fowl pox? Chicks with fowl pox can develop secondary infections, and it is harder on them than grown chickens? Have you had any chickens with MG or other respiratory disease before? What is your location, and what medications do you have around? Have there been any diseases going around in your area or state, such as bird flu or Newcastles? What are you feeding the chicks? If you lose this chick or a couple close together, keep the body cold, not frozen, and I would ask your state vet to do a necropsy to look for what is affecting them. Here is a list of state vet labs to contact for a necropsy:
https://www.metzerfarms.com/poultry-labs.html

 

[Chicharron]

Hi, yes I did see a little yellow stuff in the beaks of a couple, but I thought it was just food. I checked again later and it has gone away. It seems almost like the food gets stuck in their throats and they're not really swallowing it all. None of my other chickens ever had anything like this, even as chicks. This is the first time I've ever seen this, and I've raised chickens from babies for 5 years now.
I'm in north Texas, where mosquitoes are always a problem almost year round, including now. That's why I suspected pox. I have no idea if there are any poultry diseases going around, but we do have a problem with West Nile from the mosquitoes. I do know all my surrounding neighbors have chickens, so something could've come from one of them.
I'm feeding them 18% protein chick starter from Kalmbach. All I have for medications is Corid, Ivermectin, Nutri Drench, and Polyvisol.