Why won't my fiancé have sex with me?

Jessie
Hi ladies, I'm a newbie here. I actually downloaded this app in hope of tracking how often my sexual encounters were, because as of late I've been feeling like they are growing sparse.
A little background info: my fiancé and I are both 20 and have lived together for just over six months. We have been together for four years.
My fiancé works about ten miles away (late shifts) and hasn't passed his driving test yet, so is riding a bicycle to and from his eight hour shifts.
I've felt that, since we've moved in together, we are having sex less and less, and at times it can make me feel really conscious of myself and doubt our relationship. I'm a strong believer of loving YOURSELF first, (I masturbate daily; I struggle to sleep if I don't) and being secure in myself so as to not need sex to feel validated, but there comes a point where it gets a bit much.
We talk about the problem often: he says he is just tired or he doesn't want it as much as me and he's stressed, which I can understand with his current job situation, but even if we have a long weekend off together and I make the upmost efforts to woo him I'm often left unsuccessful. 
Other than in the bedroom, he is a wonderful, loving man. Am I being selfish? I have no doubt of his faithfulness and when I tell my friends I often get the 'I should be grateful' mentality. And I am grateful to have someone who loves me and enjoys my company as much as he says. But I'm feeling low and as much as I hate to say it: unsatisfied!
Does anyone else feel this way? I don't feel like I ask too much (id be happy if we were having sex twice a week) but sometimes I feel like I'm the only girl that has this problem!