Welcome to the Forums, Odri and your cockatiel. I am sorry for the worrying circumstances that have brought you here however.
I'm very sorry but I am not sure what the problem may be with your cockatiel, although another of our membership may have an idea. Please do bear in mind though that none of us here are avian vets so will not be able to give a 100% accurate diagnosis. Your best bet is to contact an avian vet, and the following link may help you to find one if you don't already know of one......
In my opinion it does look like something that needs a vet to diagnose and treat. Even a phone or video consultation with an avian health professional would be beneficial for your cockatiel if no vets are close by.
Thank you for joining and I wish your cockatiel a full and speedy recovery!