implantation bleeding or period?

Today I started spotting, but the flow became a bit heavier (enough for two pads). The bleeding is similar to the beginning of my period; however, just recently the bleeding has lessened significantly within the past 3 hours to barely anything (more similar to spotting). My friends have told me that sometimes the blood flow stops mid-period and comes back again (and this has happened to me, but only towards the end of my period).

I ovulated on July 6th, and had unprotected sex on July 4th (he came on my bottom, and he says none of the semen went down to my vagina) and protected sex July 5th.

I am supposed to get my period next week (30 day cycle), but it's 6 days early!! I'm paranoid because I'm not ready for a pregnancy and am currently a student in college.

I am planning to take a pregnancy test tomorrow morning, but I am wondering if it's too early to take it. What are the chances that what I have been experiencing is actually implantation bleeding and not an early period? Please help!!