I have high diastolic blood pressure for a long time now, but im young, healthy, skinny and eat well. dont know what is wrong?

Many don't: High blood pressure is sometimes related to specific definable and fixable issue. However, the majority will eventually be classified as "idiopathic" hypertension, which means we really can't explain why. Lifestyle and diet changes can help some with lower levels but some will benefit from specific medications.

Increased BP: Agree with Dr. Ferguson. Have you actually been diagnosed with hypertension or does the diastolic number just seem high to you? Hypertension isn't so common in a young person and would merit workup to see if cause can be determined and addressed.