Bloating and weight gain

I was on this med in summer of 2023 and gained 12 pounds in the first two months on being on it but JUST in my stomach. I stayed on it thinking it would pass for a few more months and it didn’t I just kept gaining weight. I have been underweight my whole life unable to gain weight even though I eat so much. So fast forward to now over a year later and ive now gained 20 pounds and it’s basically all in my stomach still. Super slow bowl movements that started out of nowhere when on this medication. My body just won’t go back to the way it was and I’m soooo confused and fed up. I am so grateful I gained weight but the placement is weird. I had a very flat stomach before this med and now I look like I’m 6th months pregnant after eating even tiny amounts of food. Tested negative for celiac and sibo even though I was so sure I had sibo. Have tried cutting out all kinds of food. The only thing that helps is barely eating WHICH IS SUCH A BAD MINDSET and that’s scaring me to think that way. Weird thing is my dietician said pristiq is actually prescribed to help digestion issues? Idkkk just want to know if anyone else had this issue and if they found any relief

Also I did notice I lost some weight when I got off the med but only 5 pounds (no change in stomach issues) Now I’m on Luvox 100mg and still feel gross and bloated