Allo.
Looking at your recent blogs, I feel that you are working in a way that's not the best for your sake. Sure, some people can work at least 2 hr+ without sweat/issue while some do have focus issue. For me, I'm good for 1 hour before I feel getting worse (worse case is headache).
Have u try taking break in-between art work/practices? Maybe try Pomodoro technique where for every 25 mins, you take a 5 mins mental break. Won't completely solve your migraine problem but at least give you some time to slightly recover and give more energy before you feel worse. Not a doctor here but it helps me when I feel that I'm gonna have a headache, both art and other work-wise.
Keep it up with your art study though. Just make sure to not take it too seriously and enjoy the process. Good luck!