Hello,
If you are 19 days late, then a test would've picked it up so I don't think it's pregnancy. Have you been thru anything very stressful lately? I've been late before with no explanation, it can happen. You are a little young to be menopausal but that is also possible. It will be hard to tell for sure without going to the doctor. I know that isn't much help, sorry. Sometimes our bodies defy explanation.
Is reaching menopause in your 30's common in your family? If your family has a history of reaching menopause young it could be the beginning of it bit if not it is more likely that some sort of stress has delayed your period.