when i came out pregnant for the 1st time, i tested positive a week later because i was cramping alot. i was about 3 wks and i started getting diahrrea and around the 4th-5th week i was getting constipated. gosh i hated being constipated i:( lol when its a very light pinkish period is when the implantation is occuring.
I would wait a couple days to see if it turns into AF. Many women that are pregnant will spot around the time that their AF is actually due. Many women also experience it right before AF actually arrives...me being one of them. It didn't happen every time but it would happen.
This is common, a lot of women myself included experience light brown/pink blood before AF is due it could just be your body getting ready to let go of everything inside. If you are late then take an HPT