When Can I Take A Pregnancy Test To Confirm If I Am Pregnant ?

I'm worried I may be pregnant but think it's too early to take an hpt. Around the 8th of last month I had unprotected sex. I'm never irregular and usually start my period on the 12th but it ended up being four days late this time, which was strange to me. I thought nothing more of it until last Tuesday, Sept. 28th, I began experiencing nausea set off by a heightened sense of smell. I only vomited once but since that day the nausea and dizziness has not subsided AT ALL, along with headaches and an abnormal amount of leukorrhea (odorless) coming out. I know some women can get their period or bleed while they are pregnant, but when would be a good time for me to take a test and get the most accurate result?