cramps in my stomach and thighs and pain in lower back the way i feel during my periods

i generally chart my ovulation which is 15-17 day but this month i did not do it. we had unprotected sex on day 6.  on day 24 i felt cramps in my stomach and thighs and pain in lower back the way i feel during my periods but my date is atleast a week out. could this be implantation sysmptoms?