you might be allergic to whatever the substances are in whatever you smoke ... if u dont treat your allergies it may stay like that for a good while even if u avoid the allergens ... i dont know there might be something else causing this, you should check out sites like
www.bloodshoteyes.org or just type in red eyes in wikipedia, i had a similar problem and i found out im allergic to a long list of tree-related thingies so i smoke spliffs very occassionally now