Diastole 50 mmhg, headache, fatigue and weakness, what this might be?

Many options: A diastolic BP of 50 can be too low depending on your overall health, body size and age. Some people with these issues might be dehydrated (common issue in Egypt in summer), anemia, or more rare issues (mast cell, addisons, vasculitis, infectious, etc.). Some doctors might suggest drinking less coffee or tea, and more plain water (but not extreme amounts). Always go see your doctor as needed.