Myth or not?

I am currently 3 days late, which could be concerning since my birth control has made me start on time if not a day or two early. A couple weeks back I missed a couple days on taking the pill and thought nothing of it. I am in a relationship and have unprotected sex. Last night I drempt of spiders and was talking about it this afternoon. My mother-in-law looked at me and told me I was pregnant because of that dream. Is it possible dreams can tell you before you know? Or is it an old tale?