Are Sporadic Headaches Caused Due To Head Injury?

My son was pushed by another kid with his forehead against a steel post.I went to emergency for a ct scan and x-rays, but the doctors told me is nothing to be concerned of, and to observe him for the next days. Three days later my son accuses sporadic headaches and only his forehead is hot...I gave him Tylenol...Do you think is something serious?