When I was on 25 mg of Zyprexa (olanzapine; usually the maximum dose is 20 mg, so it was a LOT) I didn't have my period for a couple of months. When I went back down to 20 mg it started again.
(And leave it to my male pdoc to call that 'nice' )

I didn't recall having period issues on Seroquel (I took doses up to 350 mg for about a year).