Can I be pregnant

Dr. my cycle usually comes on the 23 of every month but I was 16 days early this month.My friend and I had unprotected sex on the 6 & 7 of this month an then I started bleeding for 4 days which I normally bleed for 3 days so actually I'm 16 days early. I've only got one tube and one ovary.I went to the doctor because I've been having real bad headaches so he said my blood pressure was up so I'm taking pills, but my head still hurts and I'm always tired which he said the pills I'm taking would not cause me to become tired.So the first pregnancy test they took was neg., but he said it could be too soon to detect right know so what do you think is going on with me?