Wow, there is a lot in your post, I don't know if I can address it all at the moment, but I will say a few things:
I know that he wants so badly for things to be healthy and normal with us.
He went through a bad withdrawl when he stopped drinking entirely (a very recent thing) so I really want to believe him when he says that these bottles were just left behind.
Honestly, that does not sound to me like you DO believe him... just that you want to believe.
Lots of people in the world want to believe the best of their spouses, brothers, sisters, educators, religious leaders... but it really takes courage to stand up and insist on the truth, even when it is not what we'd like to believe. Convincing ourselves that what we'd like to be the truth IS the truth takes a lot of energy and ends up hurting people.
None of us knows if your husband is drinking again. You and he are in the best position to know. What does it mean for him to be drinking, or to stop drinking? Is his drinking a deal breaker for you? Is his lying about his drinking a deal breaker? You don't have to answer me, I just think that if you are worried about this as an ongoing problem, you should consider what it means to you.
how do I convince him that I can be trusted with the truth when I don't trust him 100%?
It might help to be honest with him-- even about your not trusting him 100%. You certainly have a better shot at getting him to trust you this way than if you tell him you trust him and he senses that you are lying.
Pregnancy is hard on everyone involved, including dads to be. I don't know where you are or what kind of prenatal care you're getting, but many midwives and even pediatricians will be happy to help you or your husband work out any fears you have about parenting or your relationship after baby-- just find someone you trust. It was my pediatrician that first got my mother into rehab when we were kids.
Take care of yourself and your precious cargo,