What Causes Vaginal Spotting Along With Nausea And Weakness After The Periods?

this is my problem: i had sex while ovulating, had a NORMAL period that same month i also took a pregnancy test and it was negative, lately i have been feeling sick, sleeping, irritated, and nauseated, i was suppose to come on my period on the 19th, i spotted on the 14th, bled regular on the 15-16, 17th and 18th was kind of light 19th spotted..and today i am back spotting..could i be pregnant or am i overthinking?