I am no expert, but both my wife and I have ADHD and currently on Medication. So I will just speak about my experiences. Our sex life goes through similar ups and downs, so you are not alone. We are both in our late 30’s and have a full schedule as well. For us, the issue was there before getting on ADHD meds, so I’m inclined to think these are more personal tendencies than being related to medication. When we do have sex, it is good, but we do go through long periods without it and initiation becomes difficult after that. We are genuinely in love and desire each other, but physical intimacy is something we work hard to maintain.
Looking at your situation, I’m inclined to think there are several combinations of issues at work. I cannot advise you directly, but I urge you to consider the following possibilities. Is his ADHD properly managed, do the two of you have differences in libido, does one or both of you have an underlying sexual dysfunction, does one or both of you have an unrealistic expectation about sex?
None of these are negative, there is a solution to all of them. One approach is counseling, either couples therapy or sex-specific counselor. We have tried several methods. One of them, as you mentioned was scheduling sex, it works moderately but the making sex a chore may not be the best thing. We encourage each other to masturbate, either solo or together; the latter usually leads to sex. We also watch erotic or adult movies to get in the mood, and we both seem to love this method.
Through this process, we discovered that my wife was bisexual and she opened up to me about her prior experiences. She assumed that I would be enraged, but I actually felt sad that I didn’t see this earlier and I wanted to be supportive. After a lot of communication and experimentation, we became polyamorous. We date and have other interactions with women regularly, ranging from plutonic to intimate. Infact until recently,, we had a live-in girlfriend. This has given us multiple avenues to fulfillment and resulted in us being closer and an increase in sexual satisfaction. This isn’t without its own set of issues and never assume adding people to your union is going to fix things. Also, this is not an advocation for cheating or swinging; this method worked for us.
I hope this helps you and you find some solutions that work for you.