What Causes Blood In Saliva During Pregnancy?

I m currently 33 weeks pregnant and sporadically I will spit blood in the morning, like it s in my saliva. My nose (snot) or whatever, has had blood the entire time and I m just stuffy. I m assuming it s because my apartment is dry and I was told it wasn t a cause for concern. I m just wondering if there is anything I can do to prevent the blood in saliva?