Undercorrection for myopia
is always better as eye can accommodate and adjust. However too much undercorrection or overcorrection can lead to ocular discomfort. But reddish eyes is not caused by myopia. Head aches and vision problems can be there because of undercorrection or over correction of myopia.
If the symptoms persist please do visit your eye doctor for refraction
and correction or to rule out any associated or some other eye diseases.