Hello Ilovedogs, it's nice to meet you. I don't really have any experience with my own children and anxiety but as a person that battles anxiety and ocd everyday I had some thoughts on your post.
Does your son's therapist specialize in ocd? Have you shared your concerns with the therapist? Is everybody on the same page, as far as what kind of treatment he should be recieving?
There are some coping techniques that he could learn that might help him, you would also have to learn these so you could help him through it. I wish I could tell you some things to help but I am really bad at not practicing these types of things.
As far as meds go, they can help but they are not a cure all, you still have to know the coping skills, I can understand why you would hesitate to start him on them but you might want to talk to a doctor about your decision. It does sound like maybe you need an appointment with his therapist to discuss his lack of progress and your expectations of how things should be going.
Like I said I have no experience with kids and anxiety, those were just some thoughts, I am really lucky as my therapist also has ocd so she is a good match for me. I hope things get better for you and your son soon.