Does this sound like implantation bleeding?

I have had a little dot of blood(super light pink) only sometimes when i wipe after peeing. It been going off and on for 6 days, it missed almost a full day and then showed up like 2hrs before bed, doesn't start till the middle of the day etc. I had protected ( we used a condom) about 12 days ago. The spots started 6 days ago. Occasionally there has been a strong twinge in my right ovary. I am also very thirsty lately. I took plan B in December, and it made me have a 28 day cycle. I have never had the exact same amount of time between a period before...but if it was to be 28days then my period would be due on the 15th. When can I take a test? I had a blood test done for pregnancy a day before the spots started. It came back negative. Is it possible to have a test done a day to soon? I don't feel pregnant..but that dot is bothering me alot.