My period isn't due for three days and this morning I started spotting brown and light pinkish blood it has no smell this hasn't happen before what do this mean? I've been feeling nausea and tired for this past week.!

Most likely you are going to start your period early. Have to wait and see. It is more common to be plus or minus a day or two, normally your period will not be perfectly on the same day each month.

Could be infection, could be a dozen things. I assume you think pregnancy, since that is where you posted this. If so you will have to wait till you fully miss a period and then test