Nexplanon. Got it about a month ago and no period.

Okay so I got on nexplanon about a month ago. When I got it my ob/gyn told me that I would start my period within the week and it would last about three months depending on the person. I spotted once. And haven't had any other blood come. I'm concerned because I haven't had a period. I've been craving chocolate and cold things like crazy within the past couple weeks. I've noticed a little weight gain... And have had hot flashes out of nowhere. Could I be pregnant or is this normal? I know they say you don't have a very high chance but you never really know?