You've stated that you do not wash your hair often. So there are a few things that might be happening 1. Product build up 2. Lack of moisture (hair loves this and gets its moisture from the shampoo and conditioning process 3. Lack of protein or too much protein. 4. Manipulation of the hair and too tight protective styles

Solutions 1. Start washing once weekly 2. Assess your hair to determine moisture protein-balance 3. I'd suggest that you switch to cleansers and conditioners that targets both moisture and protein or you try cleansers that target each variable specifically 4. Improve diet, more protein, B vitamins such as biotin and vitamin D. But, overall aim for a balanced diet. 5. Drink more water 6. If trichologist is in your area make an appointment to get your hair issues diagnosed. This should probably be number 1. 7. Be gentle with manipulation