B-T,I don't know much about Ticks,but it could possibly be related to how he feels
If he's never seen a vet since you adopted him,you should take him as soon as possible,kittens can shut down very quickly,need to eat(preferably canned food) and drink water.
I can understand you love him very much and don't want to lose him,so please get him to a vet ASAP.
Let us know how it goes,he's lucky you took him in and I
he will be ok!
Forgot to say WELCOME TO OUR FORUM!!