Implantation or Period

I need some advice guys! Two days ago in the evening I went pee to find a very very little bit of blood in the toilet. When I wiped again it came out as a super clear watery but pinkish blood that lasted maybe 30mins. I cramped in my stomach most of the night and have had lower back pain. Then the next morning I was bloated and doing the same thing as the day before, but the fluid was stretchy added on to the watery pinkish blood. I took a pregnancy test that day and the next day, both were negative. My OB said unless I miss a period I’m probably not. Right now I am 3 days away from af. My periods have been clock work as long as I can remember as well so this is quite strange for me. I’m not on any birth control and no protection is being used with my husband. As of right now I am still spotting a pink and brownish blood with lots of watery discharge, but it is such a little amount of blood that comes on and off. I don’t even see any blood in my underwear only when I wipe with toilet paper closely. I should add I have pretty heavy periods for three days, I have for almost 2 years since having my son.