Is there a healthy amount of sex my bf and I should be having?

I'd say I have a high sex drive. With my exes I was used to having sex quite often and I almost never had to make the first move (even though I like having sex I find myself a little reserved about talking about it). Anyway, my boyfriend and I have been dating roughly 7 months and we live together, he almost never wants to have sex. He's been like that since I met him so it's nothing new. But there have been a couple times where we haven't had sex for 3 weeks. He claims it's cause he's tired from work, but I feel like it's not a good enough excuse. I'm I just feeling weird about this because I've always been used to having it all the time, and I'm just not used to his lower sex drive? Or is this really odd? He'll make comments about getting a blow job, but then I joke with him saying if I got more sex he'd get more blow jobs. He just hasn't gotten the hint.