Opinions needed

My period was due 3 days ago. I have had a spot (no more then the size of a quarter) everyday since then... but no actual period. I'm nauseous and light headed and constantly hungry. I even had a weird craving for chili mac last night.

This morning I took a test and it was a super faint line with my FMU. I used First Response because the Clear Blue always seems to have a faint blue line.

I guess I'm just wondering when can you trust a faint positive? When do you call the dr?