Where did he push you? Did you hit anything with your head?

I am pretty sure that if he didnt push your head, then it is not possible to get a concussion. It takes a lot of force. But if he pushed hard, and you were unprepared, then perhaps a neck injury can be aggravated.

I have tried it a couple of times e.g. if my son runs into me when I pick him up from kindergarten, then I move my head very fast forward because he runs into my stomach. It can give me increased headache, concentration problems etc. for some days to a week, and then it "normalize".

I think anxiety is a very big player in this. I work with a therapist who specialises in CBT. I am no expert but it sounds to me that you could benefit from working with a therapist and perhaps see a PT for neck related headache?

I hope the best for you. And it WILL get better.