For storm anxiety, if benadryl is no longer working I will typically suggest a few things to consider:
1 - Thundershirts, or similar products. These are "jackets" made for dogs to hug them tightly, which can help provide anxiety relief during storms and other stressful times. One time purchase, re-usable, cheap in long run if it works. Available online, in pet stores, in vet clinics, etc.
2 - Trying a different antihistamine. But if benadryl is not effective others are not likely to help either. But it's a cheap OTC option.
3 - Meeting with a trainer. Veterinarians provide medical advice primarily, we are likely to prescribe anxiety medications, but typically can't meet with you on a regular basis in your home to work on environmental modification. See if your local vet has a trainer they recommend to help with behavior modification.
4 - Prescription anxiety medications. There are a lot of options. Some are short acting for as-needed basis when a storm is coming in only. Others are long-acting for regular administration. Getting a prescription for something like this will require a visit to your local veterinarian.
5 - DAP collars, diffusers, sprays, etc. This is a canine pheromone that can help with anxiety in some dogs. Also available in pet stores, online, vet clinics, etc.
Lots of options here, I'd suggest looking into DAP and thundershirt and scheduling to meet with your local veterinarian for a physical examination and to discuss trainer recommendations and possibly starting a prescription anxiety medication.