Could I have mold in my house?

My family and I sneeze non stop in our home. My son has nose bleeds, runny/stuffy nose, itchy eyes. In certain parts of our home (our room) my husband and I get stuffed up (clogged nose) when we lay down. It only happen when I lay down in bed when my nose clogs up and I can't breath well; my husband complains of the same thing. I can't even sleep in there anymore. This happens to our son but I'm not sure if it's his room or another part of the house. We don't have a basement except for a crawl space underneath the house. There is a water stain on the ceiling in the den because the people who rented the house before us didn't immediately inform the landlord that the cap for the wood burning stove on top of the roof flew off during a wind storm. Could this be the problem? If there's a water stain on the ceiling, could there be mold growing under it? If not, what could be causing our noses to get clogged?