I passed a greyish tissue like substance on thursday during what appears to be my period. i felt a 'gushing' sensation before i found it. it wasnt mucous, it was strong and stretchy. i had some pregnancy symptoms, e.g. swolen, tender breasts. my period was due on monday, i took a hpt on tuesday and again on friday, both were negative. if pregnancy had occured it would have only been between 2-2.5 weeks since fertilisation. what could this be?