Period

This is highly frustrating. Today is the second time I've had to tell this app my period is late. I wish my periods were regular.?? I don't know what to do. Or if I should do anything at all. My moods have been up and down and I've had headaches. I know for a fact I'm not pregnant because I'm not having sex. I'm still a vergin. Tho I have notice that my sex drive has increased a lot lately since 2 years ago when Id turned 18. Advice?