It sounds like indigestion.

Definitely if he keeps throwing up take him to the vet, but I wouldn't rush it yet, call the vet before hand and ask him/her what they would do first, so you don't have to pay for them to say "Oh he just has gas" and then having to pay money.
One thing we did with our kitties upset tummies is natural tea, we'd brew it, let it cool and then give it to them in the side of their mouths using a syringe. Not too much of course just a tiny bit. Green Tea is especially good for it because it's a very light tea and full of antioxidants, (Cats need them too)
I hope he starts feeling better soon
Update: Well, I ended up taking him to the vet because I was paranoid and scared and since these are my first kitties I want to make sure he is ok!
She took his temp, felt around in his belly, and said she could feel hard stool but no foreign objects, said he looked all around good and maybe just got into something he shouldn't have. $120 later she gave him a shot of antibiotics and sent me home with some pills for his belly.
2 days later with the pills, he has only thrown up once more, yesterday at 9am. He has not lost any appetite, still eating & drinking lots, playing with his sister, acting normal except MAYBE a little tired/upset, or maybe I am just imagining it and being paranoid!!!
He was not pooping yesterday at all, so then I got SUPER worried, but then last night at around 7pm he took a decent poo... I'm wondering if maybe he is constipated? He hasn't pooped yet today - but his poop yesterday looked relatively normal. His stomach still seems upset though, when I picked him up earlier it gurgled and got swollen

But right now he's sleeping on me with his sister.
So basically he still has some symptoms after 3 days - licking his lips as if he is nauseous, gurgling tummy (no throw up yet), and not pooping (yet). I seen him try a couple of times, but then he ended up just peeing. God I don't know what to do!! Is this something to be worried about?
my little buddy has me on pins and needles.
