Why won't my husband open up to me?

We can normally talk about anything, we literally talk about everything, I always know when somethings wrong and he's ever had a problem talking to me about it before, but know he's showing all the signs that somethings wrong, hes mood swinging, he has a really short temper, he's not eating as much all the signs that somethings on his mind and I've tried talking to him about it and asking what I can do to help and he just keeps saying there's nothing wrong, I'm starting to worry and I don't want to bug him about it and just make it worse, I'm starting to think I've done something or he doesn't trust me anymore. Please help me.