Haven't had my period since April...?

And I'm definitely not pregnant unless this is immaculate conception. I'm 17, haven't grown any, gained or lost any weight, and I'm not over stressed. I'm not over or under weight and I eat healthy and drink lots of water. I do have a bit of insomnia, so I don't get as much sleep as I should sometimes (5-7 hours on weekdays, 8-9 hours on weekends). It's nothing unusual or serious, but it's all I can think of. Is there any other reason I haven't had my period?? My last one ended around April 15th. I've always been a bit irregular, but I've never skipped a whole month. I also don't have insurance, so I can't get checked out by a doctor.