What Could Light Spotting Post Unprotected Sex Indicate?

I am of child Barry age. Gave birth to my daughter full term 9 months ago. I do have a partial bicornate uterus if this makes any difference. My obgn placed me on two different birth controls at once depopravera shot and the in plan on. I was really crampy so I got the I plan on taken out early November. My last depo shot was in September. I got my period back as normal around the 12th of Januar . And the last few days I have had very very light spotting some mixed with discharge light pink brownish. Some a more bright red. Very very little. Nothing like a period. Have had unprotected sex. But not sure this resembles pregnancy either. I just took a text tonight. And its negative. Am I pregnant? Am I testing to early? Is this just another issue all together?