Late period with all symptoms but no bleeding

Okay so a few weeks ago my boy friend ejaculated on my tummy and I was wearing pants so I'm not sure if some could have went into it pants or anything but now it's about four days after when my Peroid should be and I'm having all the symptoms of having a peroid but I'm not actually bleeding and like I know I'm not pregnant but my mind keeps saying I am can someone please tell me what's going on