Welcome to HCM!
I have read the question and it appears that the question is incomplete. still I feel that you wanted to say that after one week of that head -on - collision with your game mate you were better till you started doing your home work.
this points towards a possibility that there is difficulty in concentrating. when you were taking rest you felt fine but with a mild stressful activity only, ie., home work you developed it again.
I would advice you to visit a doctor. it can be a concussion
syndrome. your trainer Did the test but it dosent entirely rules out the possibility. More so because you felt very dizzy at that time and didn't get up at all for sometime, and later developed severe headache
Had I been treating you I would prefer going with a CAT scan to rule out anything organic behind it.
Do not fear as you do not have any movement complaint but do see a doctor once.
Hope you get well soon
Feel free to ask more question
Dr. Manisha Gopal