I’m a little confused ...??

So my periods for the past three months have been super stranger the firs month I was four days late and it only last 2.5 days the second month I was 2 days late and only lasted 2.5. This month my period was 2 days late lasted 2 days and the past three days I’ve had brown spotting I’ve taken a pregnancy test not pregnant also my periods are like clock work and usually last 7 days.. I’ve been gaining weight and my stomach is usually bloated constipation for a week then I’m going like crazy. Could something be medically wrong ? Every doc I go to won’t listen they just say I’m not pregnant but that’s not the reason I go in