I was in your shoes a few months ago, but I did not have headaches, Just fears of a brain tumor.
I also noticed the difference in my pupils. I had to go to the emergency room of the ophtalmologic hospital, to be reassured that it was nothing more than physiologic anisocoria. Having a carcinophobia made me go see another doctor, who confirmed the diagnosis.
About how your pupils change in size, that is called focus, they would dialate/constrict! That is also normal.