Pms cramping or implantation cramping?

I've never been pregnant before but I am supposed to have my period 3 days from now... I did try to conceive during my ovulation week.. I really don't know if I became lucky this time... I have been feeling mild stretch like cramping in the middle area of my very lower stomach.. I've researched n I've found out that woman can have cramping due to implantation... just hard to understand if it's implantation or pms... my pms cramping doesn't usually feel this way but lately when I cough or sneeze I have a cramp like feeling that lasts about a minute or two...it fades away but first feels like muscles inside are stretching. I haven't taken a test yet because I didn't want to get my hopes up.. just would like to know how some women experienced their implantation cramping n how it feels like if they remember... Thanks.