confused if implantation bleeding or af

did not use opks this month but af is due this Friday the 9th and I have regular 28 day cycles that last 3-4 days. yestersay the 4th I started spotting with brown than light pink. today is been red but never to fill a tampon. usually first 2 days are normal- little heavy bleeding. been having period like cramps which are bad for me. anyone experienced this and what was the outcome..I'm testing friday if af does not get heavier.