What Causes Delayed Periods?

I'm 24 year old female. Height; 5' 3" Weight: 65kg. On Jul 14th my boyfriend touched my privates with his fingers, there was no penetration. Before touching me there he touched his for a brief moment. There was definaitley no sperms as he didn't ejaculate. I don't remember if he had any precum. My period was suppose to start on aug 1st but I have no sign of it. I changed my diet and travel for 4 hours a day. I need some adivce. Thanks