help?

i’ve been mildly cramping on and off for two days in my lower abdomen and pelvic area, but no spotting. it feels like very light menstrual cramps. but my period isn’t due until the 18th according to the app. (but usually i start on 22nd or 25th so i’m unsure really.) i’m 6 days past my ovulation according to the app. does anyone know what the cause of this would be? i was thinking implantation but i’m unsure because i haven’t spotted.