First period back after breastfeeding for 8months...

Ok so I have had one period (on March 14) since I have been breastfeeding my now 8 month old and plan to continue till she is a year old... Supposed to start soon... But haven't?! Have you ladies experienced not so regular period when you first started them back? I'm kinda freaking out that I'm pregnant again even though we use the withdrawal method of birth control. Any advice?