In the 16th day of my regular 29days of menstrual cycle I started spotting and its been 3days but hasn't stopped yet even on my 19th day.is it ovulation spotting or implantation bleeding?? I'm confused.

Implantation bleeding usually goes unnoticed, if you do happen to see your implantation bleed, its mostly the size of a pin head and that's usually all, it wouldn't last for 3 days. I'm not 100% sure about ovulation bleeding, I think it can last 1-2 days.