Not a lot of sex

So recently my boyfriend hasn't really been in the mood for sex. It's gotten to the point we will start fooling around and he will stop me mid blow. I don't understand? He wanted to get me off, but when I went to return the favor he wasn't down. I asked why he didn't want to have sex with me, he said it isn't that he doesn't want to...he's just tired. There was over 2 weeks in between the last 2 times we had sex. I don't know what to think of it. I wonder if there is something wrong with me, and he tells me I'm over thinking it. Idk. I'm just confused. He's been going through some things at work and stress financially....is that a reason?