Implantation bleeding? No picture

I have a longer cycle (about 37 days) and yesterday I was spotting for the evening... This morning nothing at all so far... AF is not due until the 15th or 17th and the spotting was on the 6th of this month... Never had this happen before... The timing could be right though for implantation since had sex on June 25th and spotted 11 days later but still 9-11 days before AF... Excited and nervous. When should I take a hpt? And if it was implantation why could I have randomly spotted? Any ideas? Suggestions? Thoughts?