Suggest Treatment For Severe Hair Fall And Dandruffs

Hello sir.....genetically I was having. Very dense hair both from my father And mother side. But 2 years ago I had done very long bike rides for some very long distances continually for 2 months after that I had started very severe hair fall specially from the centre of hair .. and there is a white dandruff type of substance also settled on my head which is so much ichy . I have shaved my hair several times. But that white substance is still there. And my hair fall has also not stopped .. and it happened mostly in centre of head and also in patches my hair loss can t be genetic ..then what could be region for hair loss?and how could I stop and regrow my lost hairs.? (My present age is 23)