Take more vitiamins. My friend had the same problem and my mom talked to her mom about vitiamins. She started taking vitiamins and her problem was all better. I should say take vitiamins everyday anyways. I do and it helps with alot of things.
You could try nail strengthener. My nails tend to get weaker the longer they grow so I try to keep them filed down. Not right down, just over the tip and that seems to help.
Try using cuticle butters or creams and nail hardeners/ strengtheners.
more protien in your diet strenghtens nails
Transparent nail polish?
Vitamin E oil.