What is going on?!

Long story short: we have been trading for 6mo to get pregnant. MC/D&C Janurary, chemical April. This month O 6-18 (see chart below) extreamly sore boobs since last week. AF was originally due on 7-2, but I started spotting lightly (very lightly) 6-30 and 7-1. Nothing yesterday at all, not even a drop. This morning, NOTHING, around 7pm I took a shower and noticed literally a drop of blood...nothing to follow. Took a test this morning, completely negative. Was this an extreamly light period or could it possibly be implant ion bleeding? IF implantation bleeding how long should I wait to retest? Thank you!!!