Period Late

So I’m 17 and I’m still a virgin, but my app says my period is late by 11 days today. Earlier today I got really bad back pain out of no where, and minor cramps. I’m doing fine now, but I went to do my business earlier and saw that there was blood, so I did what every other female does and put on a pad. It’s a couple hours later and there isn’t a single drop of blood on it...should I be worried? Is this normal when you’re a teen? Could it be a change in my lifestyle? Please help so I stopped freaking out lol