So sorry to hear that about your 14 year old, that is very tough. I had a similar situation with my daughter, who eventually was diagnosed with ODD also. For me and my husband it was really hard at first, especially when we were not sure about how we were supposed to teach our daughter. We came in contact with a specialist, who told us that in order to help our daughter we needed more help than what we could possibly give as parents. When you say you are exhausted and don’t know what to do anymore, I think it’s because there isn’t something else you can do, at least not by yourself. When we finally received help from specialists, I saw results in my daughter. I found a link that I think could really help you out as it kinda describes the pressure that parents of kids with ADHD have to deal with. https://helpyourteennow.com/adhd-boarding-schools/
I wish you the best of luck! Keep being a great mom like you are!