How Can I Be Heard?

My husband has ADHD. He is currently being treated (and has been for a couple of years). We have been married for 12 years. For several years now (ever since we had children), I have felt VERY alone and unsupported in the marriage. I work full-time, but feel that I do most if not all of the childcare and housework. Whenever I ask him for help, I feel like he agrees to be more helpful and support me in any way that he can, but I am always frustrated by what seems like a real lack of effort and follow through. He is works very hard, but seems distracted and withdrawn most of the time. He is often consumed by work or projects that interest him (like finding or fixing recreational gear and equipment).  I feel that the only way he helps me around the house or with the kids is if I give him specific "orders" and then pressure him to follow through or check in on him often, which puts me in the role of oppressive supervisor and constant nag. I hate it! However, if I simply ask for help or share that I feel overwhelmed and unsupported, he tells me that I'm being difficult or completely exaggerating things, being overcritical, or being totally unfair to him and he withdraws. He has told me that he thinks I have emotional issues because of the way I feel about the marriage (ie, that the fact that I feel alone and resent him is because I have psychological problems). He feels like I emotionally blackmail him to get what I want. In fear of driving him away or upsetting him, I end up doing the work myself and resenting him for not being more of a partner. I believe that he wants to help, but I feel so alone and don't know how to get him more involved in the home and family. Perhaps he doesn't want to help and I need to accept that? Does he just want to be left alone? Am I really alone in my marriage? Anyone else experience this?