Not sure if this is called "stretching"...please help?

ok so my period usually comes around the same day of every month... well in april i didn't come at all but i did start on like may 2 or 3rd cant really remember...well today is thursday n on monday i was having these weird menstrual cramps but they were making me feel like i had to poop an i kinda felt a little nausea ( sorry tmi ) they were coming about once every hour just about the whole day...when i was telling my sis n law about it she said it sounded like i was stretching which i guess means when the fertilized egg attaches itself to the uterus it then begins to stretch to make room for the baby..me n my fiance have been ttc for awhile now n i know my period is late but since it was off last month im not sure how many days it exactly is late...so i could be prego or what do u think?? i took a hpt yesterday and it was negative so i could be prego n jus not far along enough to show up or idk....btw that was the only day these cramps appeared..please help