What Causes Light Vaginal Spotting Along With Tiredness Post Menstruation?

i had unprotected sex with my boyfriend about a week ago. And it was on my period to. My period lasted about 3-5 days i can t remember, but when my period stopped the day after i saw some light spotting,lasted a couple of hours,iv been very tired, have a feeling that i want to throw up but nothing comes out, have light cramps, could i be pregnant? its only been a week though.