It is very difficult to self-diagnose pupil size and reactions. If this has you concerned, an office visit with a doctor may be worthwhile. There are a few conditions that can cause this but a concussion is not one of the common long term causes. In other words, a concussion two years ago would not cause it now. One condition is Horner's Syndrome. It is rare and has a myriad of causes.

If you develop a building headache that gets intense, have somebody give you a ride to the emergency department at the hospital.
(edit) I forgot to include, this dangerous headache would also usually be accompanied by any form of speaking, smiling, or other muscle control losses.

For some, a mild version of this condition is ideopathic (cause unknown) and may have even existed prior to a suspected injury.