Vomiting cat with constipation

I've had my cat for about 13 years. I came home for Christmas break from school and found out that he has been constipated for the past few days and is throwing up when he does eat. This morning, he has been acting strange; he has been trying to go to the bathroom in various rooms of the house (he's never done that before), when he does go into the litter box he hisses after leaving, and he has been meowing and yowling much more often than usual. It's Christmas, so I can't take him to the vet today, but I was wondering if anyone had any idea as to what could be wrong or what I should do. Thank you in advance for any advice.

He sounds as if he has some sort of blockage, and I'd look for an emergency clinic at once. Only a vet will know for sure.

Please get him to the emergency vet ASAP.

I would not play around with my own ideas of helping a possible blockage, there is too much at stake. Please at least call an emergency vet and see if they will give you info to tide you over until you can get to your own vet.

Thanks. I have an appointment today, so hopefully something is figured out.

Good luck and best wishes for kitty