possible late period, pregnant?

Hi , im only 17...im scared that my girlfriend might be pregnant although i do not see how..me and her never had sex sex but weve done other stuff before and today is day 31 and she still hasnt received her period yet. Her last period was competely normal and im not sure if this one is late or not because she never keeps track of her cycle...so i may be wrong. She feels bloated and craves certain foods as well as random mood swings and she is starting to gain pimples although not much..She thought she as gaining weight but the weird thing is she actually lost weight, like 5 pounds. SHould i be worried or not...what do yall think please answer asap im really worried as of now even though there really isnt a chance.. thanks

Irregular periods for pre-teens and teenage girls are pretty common. When I was younger I would get mine months apart and sometimes only 2 or 3 times a year. That being said hormonal imbalances are also common which would cause those things.