Was it a possible miscarriage or normal menstrual?

I woke up this morning feeling very ill. My stomach was cramping really bad & I felt weak (dizzy, light headed). As soon as I went into the bathroom I started to urinate and then there was one drop of blood then a big grey-ish blood covered "glob" or sac dropped into the toilet from me. I am/was expecting my period at the end of this week. I engaged in unprotected sex 2 weeks ago for the first time in a while and was wondering is it really possible that I could've been pregnant and miscarried THAT quickly? Everywhere I looked from Google said it was likely a miscarriage.