Hello I wonder whether your kitten may have a respiratory infection, such as cat flu. Cat flu is viral but the insult to the immune system can leave kittens very weak and prone to secondary bacterial infection too. It can be fatal. There are some therapies that are not medical - for example, steam inhalation (administered correctly and safely - ask your vet) can clear the airways, resulting in relief for small periods. Good nursing including keeping the patient warm and the provision of small, frequent meals (served slightly warmer than room temperature), often may be helpful. It is vital that such kittens take plenty of water (soaking of food or biscuits may help) because such kittens are often very prone to dehydration. Water should not be forced into the mouth because of the risk of aspiration pneumonia. For the best chance of survival and encouragement to thrive, a kitten would likely benefit a lot from seeing a vet, in order that medical treatment (drugs) specific to their needs can be given. Cat flu can lead to eye ulcers, for example, which can be sore and lead to blindness, so eye drops may be needed. For more information about cat flu,
see the Factsheet.
I hear that cost to cover veterinary treatment is a concern and would encourage you to call charities, such as the RSPCA or cats protection league in the UK.
I hope that something here will be helpful.