How do you know if you have lice?

I had lice because my friend had it and her mom treated me. Now I recently had a sleepover with her but I wasn't sure if she was clean I'm at the point that I'm so paranoid I keep checking in the mirror. I recently popped something in my hair but I got scared and release it but that's when I just woke up. Please help do I have lice? I itch there and there but not constantly. Am I just paranoid?