Strong cramping

Yesterday I had a very strong cramp in my lower abdomen. It was very painful and lasted for about a minute. It was so strong it reminded me of labour contractions, I even had to breathe through it. This morning the same happened. Other than these 2 isolated episodes, I have no other symptoms or pains. I am 6 dpo and 7 days away from my period. What could this be? I heard implantation pain is usually a dull pain and lasts longer, so I'm not sure.