Do you think he's cheating on me?

it could be that he is cheating on you, but it also could be that he is telling the truth, you never know. so, what i think you should do is keep doing what you are doing, like calling him and stuff, if it keeps happening then id say yes he is, but try to get more info together, that way you have more to front him on if it comes down to asking him.. then he most likely will tell you the truth.