How long is your cycle,on a 28 day cycle you been due the 18th,so maybe the bleeding you had was a period,sometimes we can have strange periods.mine now only last 2-3 days tops,and somtimes really light.not everyone has implantation bleeding.i would see if your next cycle comes or maybe test in another few days,good luck.
Well they say implantation bleeding/spotting can occur any where from a week to a few days b4 your expected period. This is my 5th pregnancy & the 1st time I had implantation spotting. I noticed it about a week after DH & I bd. & it was also about a week b4 my period was supposed to start. Your period still hasn't started? Then, I would retest today & then again in 3 more days if it doesn't start.