How old is your boy?
Is he vomiting after eating or just randomly during the day?
How long has the vomiting been going on?
Is he neutered?
Does he go outdoors?
Is he eating and drinking?
Is he having any problems with the litter box - staying in it for longer periods or making frequent trips to it?
He may just have an upset stomach. Since this has JUST started, I wouldn't be too worried yet. Cats seem to vomit more than any other species and the crying before he vomits is normal, Krista. I would leave him plenty of water down this morning and not give him anything to eat for about 12 hours to let his tummy rest. Give him a small amount of food this evening to see if he is able to keep it down. He may also have a hairball that he's unable to get up that is causing the vomiting. You can go to the pet supply store and get some laxatone for him, or put a small finger-full of plain Vaseline on his front foot for him to lick off. This will help him get the hairball up if that is the problem. If he is still vomiting in the morning, you need to call your vet and let them know what is going on. They may want to see him.
Please let me know if I can help further.