Please don't laugh:

I am on my fourth month of Yaz, and haven't missed one pill. However, last Saturday I had a brownish breakthrough bleeding, which stopped, and now I've had slight brownish discharge for two days. I am terrified of getting pregnant, and take my pill so diligently. My period is due in 6 days, and am going to run out and take a test tomorrow. I feel really tired, have a headache, and feel bloated. Has anyone had this experience, worried sick over being pregnant despite being on the Pill?