i do not personally think varying pupil sizes are likely do be due to sinus problems. the headaches could, however.
i also do not think your specific pupil descriptions could be due to brain tumor or aneurisym. aneurisym causes a "blown" pupil...a pupil that is much larger and does not work. that is not what you are describing. tumors cause pupil constriction problems that would be obvious on an eye exam.
if you are really worried about it, go see a neurologist. but for a young lady to have varying pupil sizes does not sound too concerning. especially if nothing was found on an eye exam. if both pupils work (constrict) and you do not have an afferent pupillary defect (which i'm sure both your eye doc and your family doc both ruled out as soon as you complained of varying pupil size), then it is highly unlikely IMO that anything serious is going on with your eyes.