What Causes Spotting With Brownish Color Post Menses?

i had my period about 2 weeks ago, it was pretty heavy. i'm irregular and i was also diagnosed with hpv. last night, i was spotting with brownish color and a bit of that mucus discharge with no smell. earlier it was brownish, now it's getting brighter. i'm feeling a bit of cramping too. i also took a pregnancy test because i have been real emotional and feeling nausea. the pregnancy test came out negative. i'm guessing i'm stress, but i'm not sure.