Id just talk to him about it. Thats really the only thing you can do.
men get pregnancy symptoms too, maybe he's afraid of hurting the baby? i know how you feel, my partner is depressed (because he's not working and looking for a job, and feels useless, and wants to work) and he doesn't initiate it much either, and rejects me sometimes aswell... just have a talk with him, like a proper talk, don't let him avoid the subject, see if anything else is bothering him, stress, work, harming the baby, not being comfy with the bump... say that you're not happy with it, and that it really bothers you, and you're worried he's not interested in you, have a talk with him...
i feel bad about it too, but i try to understand and support him, with his stress over worrying about money to much, and his tablets for depression aren't doing a good job at helping him getting aroused :(