If you have tried everything and absolutely nothing is working then maybe it is an underlying medical issue, maybe you could have a talk with your doctor and she may refer you to someone else.
Certain medical conditions such as malnutrition, hypothyroidism, Menkes syndrome, and some illnesses that affect your hormone levels or unbalanced hormone levels on their own can cause very dry brittle hair. If it is a becoming a big problem and you have to keep cutting your hair I would get checked out.