I've had trouble with my eyes all this pregnancy, but it's been gradual changes, not that sudden. Making sure my eyes don't get too dry helps.

I'd try using some lubricating eyedrops, one of the ones with no preservatives or anything in them, that you twist off the little plastic cap and use each dose just once.

If better lubrication doesn't work, I'd call the doctor. Such a sudden change might be indicative of something more serious.