Be sure you are taking the Benadryl that does not have pseudophedrine it it. That Benedryl will increase anxiety.
Since a psychiatrist usually does not provide therapy, it is fine for you and your son to have the same psychiatrist.
Family therapy, or a therapist who will see both you and your son might be helpful. This works well when it is something the therapist specializes in. I did this when my son was a teen and it was very helpful to us as a family. I never prodded my son about his therapy and the therapist never divulged anything they talked about, without asking my son ahead of time. I respected that and it was a good thing for my son to see, that adults were respectful of privacy and a person's wishes for confidentiality. Sometimes younger persons don't get to see examples of that in their 'young persons world'.

I hope your son and you feel much better soon.