Caspian is a syrian hamster, I've only had him for 1 and a half months, he has this weird bump on his right side, just around his stomach, it's quite big actually. He also has green poop, which I think is very weird. He's eating and drinking normally, and if I take him out he'll run around like usual. He's had this bump for about a week. What's wrong with him?

And when I touch the bump he doesn't do anything!

Hamsters are prone to cancer, especially syrians. The only way to know for sure what's going on is to take your hamster to the vet. It could be cancer, it could be an abscess, it could be anything. Testing will have to be done, which we really can't do on the internet.