Oh yes, diet related health issues are so hard to get used to. I have milk protein allergy and IBS (which apparently is similar to fructose malabsorption, at least regarding symptoms). So yeah, I totally understand your pain.
Also, I hate how most doctors can't be bothered to take the time and make a proper diagnosis for smaller diseases like this. It took me 6 years to get the diagnosis for IBS, and all that time it felt like most of them didn't even bother to listen when I said that yes, there IS something wrong with me, I'm not coming here just to complain about a small stomach flu. Even now I don't get any kind of treatment for it, I've pretty much learned a good diet for myself through trial and error (and even so, during bad weeks or months, nothing helps).
Anyway, enough with the rant.
I think the idea of doing speedpaints is a good one. If you limit your time and learn to stick with it, you might start finding new ways of painting things faster. It looks like you're already a pro at sketching, so you should perhaps just practice working with colour and shapes instead.
Maybe even do a few pieces where you don't sketch the character beforehand, but instead just start working with solid blocks of colour and then go from there.
I'm glad I could help to make you feel better! And as cheesy as it sounds... always remember, you're not alone. Most people do understand how life can sometimes get in the way of doing things you'd rather be doing.