Is it bad to take unperscribed medicine to aid sleep?

Okay so I'm 14 and I have insomnia. My doctor didn't want to put me on sleep pills because I'm so young. He said to take Benadryl on rare occasions if I really can't sleep. It worked and now I just take it pretty much every night. Sometimes I take Nyquil or Tylenol PM too. But that's usually only when I have a bit of a cold. Benadryl is my main sleep aid. Is it bad to be doing this or is it okay?