This morning I had brown very light discharge, it went away.. now I have pinkish watery discharge almost as heavy as a normal period (due in 3 days)... had sex day after ovulation and have had cramps since... it has been 9 days since.. could this be implantation bleeding(medium flow)

Possible, but more likely period getting ready to start. Pregnancy is best achieved if you have sex in the days right before ovulation because it can be very easy to miss the window of opportunity.

See what happens when your period is due. Give it several extra days if it is late and try a test if it doesn't show up or is different from the norm for you... such as fewer days in length and lighter flow.