Why dont i have any PMS this month?

A week to 2 weeks before my period is about to come i have really really painfull and period pains. my period is 31 - 36 days and should start soon but i dont feel that i am? i had a few pains 3-4 days ago but nothing now? this is strange for me? anyone else experienced the same then found out they were pregnant? what week of pregancy do your s start hurting?