When to take a test

Okay so I have been feeling off lately, and as my period was supposed to come around all thr normal excrusiating pain I get right before my period I dont have at all. My period was supposed to start yesterday and i had unprotected sex twice within the past month and a half. I need help because I nees to know when to start worrying. I am only 18 and the guy and I are not dating(hes the same age).

UPDATE: my period started this morning. But I still feel off because normally I'm in excruciating pain because of cramps and none of my normal pre period things happened. Something just doesnt feel right. I should be thankful I'm not in pain but I have always been in pain during my period so its concerning to me. Any advice?.