I'm 16 years old and i take 3 tablets of benadryl (diphenhydramine) every night because i have a very hard time sleeping is that okay ? i take 3 because 2 doesn't work!

No: No it is not okay. You need to find out the cause of the sleep issues and then take steps to correct it. Continuing to rely on sedation at age 16 is not good.

See your doctor: Taking pills every night, to help you sleep at the age of 16y is not a good idea. If you have sleeping problem that lasts for more than 1 week, you need to see your doctor. You are already seeing one of the side effects of Benadryl, (diphenhydramine) that is acclimatization. This means that you need higher and higher dose to get the same effect. Better to consult your doctor for a more appropriate management.

No problem: It you don't have side effects such as excessive drowsiness the next morning or dry mouth, I see no problem with it. However you should try to improve your sleep habit but not drinking anything with caffeine after noon, doing or watching anything too exciting before bedtime, and dimming the light in your room near bedtime etc