What Causes Spotting With A Negative Pregnancy Test?

I want to know something doc, i just wanna know if i'm pregnant.,my period should be today February 10, but last first week of February found spot on my underwear,and i thought i'm going to have my period early, but nothings happened..and yesterday when i pee, after washing there's at least 3 drops of blood dropped of the floor.,its not light red or brownish, its totally red,..And before i forgot i have a U.T.I now, and to hard to pee.and i try to test if i'm pregnant yesterday morning..and it's negative.,