I don't think you have messed up and there is still time. In this situation, the meds can help take the edge off so he can refocus. It sounds to me like his frustration at not finding a focus is coupling with a guilt over the fact that he can't figure out how to express this frustration in a "socially acceptable" way. one of the things those of us with add struggle with daily is a deep seated need to be accepted. We need that like air, because we feel we are different right from the get go. We feel like round pegs trying to fit into square holes, and it doesn't work for us, yet the expectation is that we must fit in, that there is something wrong with us if we don't. Problem is that we never will. Academic institutions for the most part cater to the lowest common denominator of intellect and creativity, as well as putting boundaries and limitations on all students to prepare them for their role in society. This is not a bad thing, but it is an impossible task for an add child to cope with. We don't perceive boundaries and limitations, any more than someone that is color blind can perceive the colors that their eyes are not capable of seeing. No amount of punishment or reward or cajoling or wishing will make it happen. We live in a completely other paradigm altogether.
Practical advice from an adult add? Get the meds so he can decompress a bit. Help him find a focus. For me it was music. Observe him closely, and when he shows an interest in something, encourage it. Help him understand that there is nothing wrong with him. He is not sick. Add is not an illness. It's not a chemical imbalance, although chemical imbalances can make it worse, as in my case. Add is a gift, and it should be communicated to him that as with all gifts, it's up to him to find out how to apply it. And above all, touch and love him, no matter what. We need touch. We need love. A gentle touch during a frustration period can calm and soothe him fast. When he's adjusted to who and what he is, let him decide to leave the meds behind or continue. The teen years are the worst, so he may need them til his 20's or beyond. Also, I recommend that you read everything you can get your hands on about the Indigo children. That will help you learn to help him.

Bright Blessings
Dr. Jasper Goodnow