Hello! I would like to try and help you help your dog. Fireworks can be very scary for them. If they are happening right now, I have a few suggestions that may help some. To start with, you may be able to increase the amount of diazepam that he is on. I don't know how big he is or what dose he is on, so I can't tell you how much more you could give. You may want to contact your prescribing veterinarian. Simple things that may help him would be to have him in a room that you can close shutters, turn on a tv or radio rather loud, even place some cotton in his ears (remembering to take it out afterwards!). This will all help reduce the sound. He will still be able to feel them if they are close by, though. For future fireworks (and other scary situations), I would recommend that you look into getting something like a Thundershirt for him, as well as looking into a product such as Adaptil, a calming pheromone spray. You can find information on both of these products on-line. For tonight, a snug t-shirt may act somewhat like a Thundershirt, applying full-body pressure on him which often does help them feel calmer, like a full-body hug.
Try keeping him company and trying to distract him with some of his favorite treats in a dimly lit room with covered windows.
I sure help that some of this helps this evening, but hopefully gives you a few ideas that may be used in the future. Good luck! If you have any other questions or if there is anything else I may help with, please let me know.