I have been diagnosed with ADHD, although there are two very different opinions from two different doctors. One says yes I am (inattentive type with some sensory processing disorder), the other says probably not but won't rule it out completely. Needless to say, I'm confused on the matter of their opinion, but have enough self awareness to know that at least I have some kind of problem that needed solving in order to lead a better quality of life. Missing deadlines is NOT ideal in the freelance world and you will not get work if you don't find a way to shape up!
And focus was my biggest problem. So earlier this year I requested a referral to see a psychiatrist who specializes in ADHD (she is the one who doesn't think it's my problem and attributed my issues to anxiety/depression). We have had several sessions and for this and other reasons, she has suggested I try medication. One to manage the depression/anxiety, the other to manage something I do not wish to disclose here, but it is also prescribed for people who have ADHD.
I don't condone medication as a solution - most of the time it is simply a bandaid for something that might have healthier or more natural way to solve the problem. I was, however, at my wits end and too far into my life to feel like a complete and utter failure anymore. Mindset tools such as Cognitive Behavioural Therapy, Neural Linguistic Programming, Acceptance and Commitment Therapy haven't quite done the trick, though they have added to my arsenal of how to deal with issues that come up. The same with learning how habits work and how to replace/build new and helpful habits, and just understanding my own brain and how it works!
Truthfully, it really has made significant changes for me in the past few months. I can stay focused, my mind is not racing all over the place to every shiny possibility. I have been able to maintain my concentration to a point where I am getting through online class lessons and better yet, GETTING THINGS DONE. I've finished a lot of art where as before, my WIP folder took up most of the space on my hard-drive. Consequently, my confidence in my abilities has increased too.
Meds are not the be all and end all. I combine this with support from my psych, accountability to friends and mentors, lists, notes and goal setting to stay on track. I have a lot of ideas and I make notes about them in a notebook or file, somewhere I can see and sort them out. I have reminders and alarms galore. And although I haven't completely mastered all this, the difference is amazing and I'm extremely happy with the progress.
It is up to you to find out and manage how you process things. Try everything till you find something that fits, there are heaps of tools available to help focus, time management, etc. It's a bit of an adventure finding these things out too. With your art, others have made some useful points, so I won't repeat them, but it also may not be a bad idea to talk to someone about how you can find a way through this. Because if you really enjoy drawing, you will no doubt keep coming back to it, even after a bad art block or hiatus. Accepting that you are creative and identifying it with yourself is also helpful, so say "I AM an artist" instead of "I'm not an artist", no matter what your skill level. If it's what you really want to do, you will naturally feel pulled to do it at some point.
Sorry... I am also incredibly long-winded, but this topic resonated with me, so I hope it helps... you or anyone who reads and has similar quirks. As others have said, dig deep and find out about yourself. Talk to your doctor about managing any flighty tendencies. Research. Practice. And hopefully you will find the answer you seek.