my phone goes from 5% to 9% in just a few seconds when i charge it

so basicaly i have this problem after i shut down my phone after charging it , i read that you need to shut down your phone for a few minutes once a week , i charged my phone one day , i unplugged it at 89% i let it be for a few minutes then i turned of my phone for 7 minutes..when i turned on my phone again my battery procentaje was on 93% .. from that moment and now everytime when i put my phone at charging it goes for example from 5% to 9% in just a few seconds.. the same thing happens when i put my phone at charging at 2-3 % it goes 1% down then is charging normally... and when i turn off ,y phone and then turn it up again it charge few procentajes..the awkward part is that i am the only one that have this problem and my phone is new..but it goes down on battery life from 100% to 97 in just a month after the ios 14 :) and i am not that kind of person using the battery too much but my phone kept getting down procentajes..now my phone health is at 97%.. i want to know that is a problem with my phone