Struggling with Chronic Constipation Diagnosis

I was finally able to get tested for Hirschsprungs Disease and after trying to get tested for basically 20 years (when i was a baby my parents fought for that test but Childrens Mercy never tested me & now that im able to advocate for myself i had been asking to get tested for HD) but after all that the test results were negative (or "normal") I have all the ganglian cells on all layers. and I cant help but feel extremely disappointed. Like I didnt want to have Hirschprungs or have the surgery to fix it, I just want an answer for why I have this chronic lifelong constipation and now that I know for sure that I dont have Hirschsprungs I just dont know what it could be and I feel lost and very upset that I'm right back where I started with basically no answers. My Doctor said I should keep doing Pelvic Floor Physical Therapy but I honestly dont think this will "fix" anything, like it helps some but not lots. I just feel disappointed and like I will actually have to be on 4+ laxatives for the rest of my life. I'm slowly lowering my Merilax and if I'm able to get to less than 1 capful a day my PT says I should try to incorporate more fiber in my diet. Which to me is a very upsetting thing to talk about doing since, in the past, Childrens Mercys GI Doctors said I should up my fiber and take fiber supplements (and told me lots of other bad advice that made me feel like they didnt even listen to me) which only caused me to get extremely constipated and almost hospitalized because it got so bad (I had to do a multi week clean out to try to get it under control after, and I had only tried to fiber diet for a week and just that long made it that bad). I just feel like I'm right back where I started and I feel kind of hopeless to be honest.