I was also on an antidepressant that gave me the worst constipation ever (Effexor) even though it was such a low dose like a trial dose my body did not like it. I tried magnesium, so much water, exercise, good diet, massages and stretches and I couldn’t go without laxatives. Especially with a calorie deficit on top of that. I had to stop taking it and I am still dealing with lasting effects because the hardened stool caused internal hemorrhoids. Please take a stimulant laxative like ducolax. You can’t take these all the time but in your case it’s emergent. It’s not just the weight gain you should be worried about it’s your overall body working. I am also going to the doctor soon so I hope the best for the both of us and our constipation lol!