Use of minioxdil. Doctor prescribe it?

If we stop minioxdil than why hairfall occurs? than why does doctor prescribe it ? I was having just a small hair thinning in front of my head which was really small I went to doctor he prescribed me minioxdil I shed a lot during minioxdil used for 4 month so I stopped it but now also I am shedding a lot and it's has been 4 month now so was this mean for extra shedding or what I did not losse my hair like this ever now they are very weak and fragile so much that when I run my hands over my hairs I get 3-5 strands of hairs very easily in my hand now I just want to stop this minioxdil shed and if it is not due to minioxdil than what can be the reason due to sudden start of hairfall while u are on minioxdil and that starts again after quitting minioxdil for one month and regarding harmones therapy my harmones are doing well because no other problems related to harmones I was also prescribed certain vitamins like hair fact and adgain along with minioxdil so please give specific answer