Implantation bleeding?

Hi I had some VERY light old blood from the 16th-19th. My period isn't predicted to start until tomorrow the 23rd. My bleeding was all old blood and wasn't even enough to fill a small panty liner on the 16th. The 17th through the 19th it only happened when I would wipe in the morning nothing for the rest of the day. Could this be implantation bleeding? I took a test on the 19. I think I saw a faint line my husband said it looked negative. When should I re test? Having quiet a few signs of early pregnancy.

Update: Tested on Monday morning and it was negative. Period was due and I'm now late 2days. Well two days if I don't start in the next 2hours. pregnancy like symptoms have increased. My breasts hurt so bad I could cry. I normally don't get this before a period. When should I re test?

Update: Re tested last week and got a bfp! See the Dr next week and will have a bedside ultrasound as well. App says I'm about 7 weeks. No idea why it would take so long to get a positive. Next week can't come soon enough!