I have a cat

Get his health problems sorted with the vets or you can buy over the counter flea treatment and worming treatment. By the sounds of it you may struggle to administer them though if he is not coming out of his hiding place, so a vet is probably your best choice. If he’s hiding it means he’s scared. Hopefully once treated he may be a bit less irritable. But with a rescue cat you need to give patience and understanding. Talk to him in a soft positive loving voice, hopefully after hearing you for some time he will get used to your voice then encourage him out with treats and things he like. Once you get some sort of chance to see him if he lets you try to stroke gently giving the positive voice and hopefully he will feel safe and secure around you

He needs a flea bath then get him flea repellent drops, you can get it at Walmart or any pet store. One squirt on the skin behind his head and he’ll be free of fleas for 3 months or more and the drops will kill any eggs that are on him.

To check for fleas look through his fur at his skin, if you don’t see any fleas take a wet paper towel and wipe vigorously around the base of his tail.
If the towel is reddish or blackish then he has fleas.
Fleas constantly bite and can make him very sensitive and skittish because of the anxiety and stress.

You should treat his fleas, here in Ukraine we usually just give them a pill, or two in short succession if needed. I think it's a terrible idea to give your cat a bath, since he's already so scared and was possibly mistreated by his previous owners. Maybe take him to a vet and let them do it, so it doesn't make him lose trust in you. Remember to wash all your sheets and such afterwards so that the fleas don't just come back. About him being shy, I think you just need to give him time and space. Don't try to approach him, maybe people kept taking him up before, so if he understands that you're not going to bother him, he might start to trust you and come you by himself. You could carry some treats that he likes, and if you notice him then leave them somewhere close to you so that he'll come a little closer by himself and find out faster that you're not a threat to him. He will come around eventually but it takes time. 🩷

There’s a pill called Capstar. You can buy it over the counter (in store or online without a prescription). It starts killing fleas within 30 minutes, and it is short lived. It only works for a day or two, but it can give some immediate relief until you get a more long-term flea med.
You could put it into some wet food or fish, some high value food, because pilling a cat can be really difficult.

If he is infested with fleas, he also has tapeworms. I had such a cat. You have to take him to the vet and get a professional flea treatment for him, and get him checked for tapeworm. You also have to have your home sprayed or treated for the fleas, or else they will eventually start biting YOU.

@mellie 😯i hope not as a cat owner i find that scenario appalling maybe why it is timid 🤷‍♂️might be its new surrounds too

He will comeout eventually