My Kitties are acting strange

Faylina M asked:

I got this new kitten a few weeks ago, we took him to the vet because he was sneezing all the time, vet said he had a small kitten cold and we had him on antibiotics and it seemed to go away. For a couple of days he was running around playing with our other aniaml (a full grown 3 year old cat).Now my kitten is very depressed looking, doesn't want to move, eat, drink, or go to the bathroom, he has urinated once but thats it. In the past my cat had a problem with hair balls (my other one) so i gave me kitten a teaspoon of veg oil to see if maybe he had a hairball but to no avail he STILL won't go to the potty.

The other problem is my 3 yr old cat is now sneezing a good bit, like my kitten was when she was sick. Other then that shes fine, playful and otherwise normal.

How long should I wait before I take my kitten to the vet, should i do it immediately? Hes also from a animal rescue if thats helpful.

Should I worry about the minor sneezing of my other cat?

Please help!!!
More info:

My kitten two days ago vomited a few times but we figured its because he gorged himself on food (which he WAS doing)

My kitten was neg for feline luk when in the animal shelter and my other day is vaccinated but was at one point around cats who were FL positive.

Should there be concern for this that they both might have FL?

My kitten was also gaining weight until the day he vomited and now seems hes back down to where he was two weeks ago when I got him.

Hes about 15 weeks old.
I decided to call my Vet while I was waiting for responses. I am taking my kitten to the Vet today. My cat doesn't need to go to the vet but will take her in if she doesn't get over the sneezing.

It sounds like your cat has some health issues. Your best is to take your kitty to a vet for a full check up.