What Causes Irregular Periods And Brown Spotting After Having Safe Sex?

I have been having unprocted sex a few times in the past three weeks, my period came a day late but it was really light the 1st day with brown blood and spotting, the second day it was a little heavier, now this morning (the third day) I am having regular bleeding but it is bright neon orange...please help me! is it too soon to take a pregnancy test...what else could this be?