Talk to Dermatologist on No Hair Growth And Volume

I have been facing my hair problems since 8-9 years but from past 5 years my hair are losing their shine. Growth has been stopped since 10 yrs and now no oil no serum no diet is fixing it. Iron and b12 tests are low but my question is my paternal and maternal sisters have severely low iron and b12 levels than me then why their hair are thick voluminous and have best growth?