How do I know it's working

Scarlett

Ok so I have had my iud since last May but just last month me and my bf decided we were ready and I let him cum in me (that was also the first time I ever let a guy do that) and now it's getting close to the time that I should be getting my period and I'm kinda freaking out like I just want it to come already and I know the iud is suppose to be 99% affective but I am still really scared so what does everyone think am I just over reacting?