late period

so i’m 17 and my periods are almost always normal and spot on. i’m on my third day of being late. i really do not know what is happening. i know that it could be a hormonal thing and i am almost certain im not pregnant because i have an iud which is supposed to be the most effective. but there’s still a chance i guess. i just don’t know what to do. i’m not cramping much. just a little here and there but it’s not as severe as it usually would be. any tips or some advice?