Your question could not be more timely. I have had one cold/flu/sinus infection after another for the last 6 weeks, and got out of the habit of practicing. It used to be like brushing my teeth. After dinner was done and the dishes were put away, I practiced. And, I didn't even have to think about it, I just did it.
After 6 weeks of pretty much working, then vegging, I'm out of the practice of practice. 6 minutes seems to be all the focused attention I can bring to the keyboard. So, I'm building up slowly. First those 6 minutes, then adding 5 minutes each time I sit down. Now, I'm routinely back up to 45 minutes to an hour each day.
Perhaps if afterschool isn't working for you, try before school. When I have meetings in the evening or some time to spend tutoring our son (who also has issues), I know that I'm not going to practice at 10 p.m. when I get home or 8 p.m. if we've spent a long time working on some big project. I will practice at 5:30 a.m. (which I know sounds brutal), but then I know that it is done for the day.
Finally, if it bothers you that you aren't motivated to practice, you are still a serious student. If it doesn't bother you, then it is time to take up another activity!