Two of my 4 are afraid of the thunder and lightening too.

Rescue Remedy was suggested to me as well as Melatonin. Perhaps you could speak with your vet about trying either of those or just get some and try it. I don't know about how much of either you should try.

I'll admit I have given Zipper and Lilly Benadryl before to try to settle them a bit and I always turn on the radio to distract them. I worry about the storms that come up when I am not here, though. It is a constant concern and I really think that Zipper probably became a stray due to a thunderstorm and maybe being outdoors while it was happening. He really does freak out.