Implantation bleeding at 15 DPO??

Hi ladies. :o)

Just wondering if any of you have experienced implantation bleeding later in your cycle? I usually have a very spot-on 28 days cycle with a 13 day luteal phase. I ovulated on 3 May, and was due for my period yesterday (17 May). Usually my cramping starts the night before my period is due, with AF rearing her ugly head by the morning pinpointed by Fertility Friend. However, there was no cramping Saturday night for me! Or yesterday, despite me dreading it every second.

It's now well into Monday night and I still don't have any cramping. When I went to the toilet after dinner I noticed a tiny bit of dark brown discharge on the tp - definitely not my period but a bit worrisome nevertheless! I took a HPT this morning and it was negative, but of course it would have been if implantation only occurred, say, yesterday or this morning.

I have been feeling extremely dizzy/lightheaded for the past week or so on and off, have been smelling weird things and have this weird 'full' feeling in my belly. Does this sound familiar to anyone, or am I hopeful due to the lateness of my usually prompt AF?

:o)