Cramping and shooting pains in breast CD20?

Nicole • Married June 2013 • FTM March 6/17
Ive had period like cramps for a couple hours today on CD 20 and sharp shooting pains on and off in alternating breasts, which started CD 19. I'm pretty sure that I'm only 3dpo so isn't that too early for pregnancy symptoms? Implantation or O?