Could just be how your body works & how it reacts & respond to different things. I sometimes weigh more after I poop than I do immediately before - weird.
Yes, exercise only contributes 10-20% of the weight you have to lose (though I read recently it’s only 5%). Personally I never exercised throughout the my whole weight loss journey & I lost all & more of my weight. I’ve tried all sorts of exercise programs over the years. Never really enjoyed any of them & they never helped me lose or maintain weight. Hate sweating & have never reached that exercise high people talk about. Never felt great like you do just icky & exhausted. More likely to have a drop in my blood pressure & a hypoglycaemic episode. ☹️
I do a few minutes of gentle stretches at night more for my back than anything else. Wouldn’t burn 20 calories 😆. I do do incidental activities like park further away from where I’m going, take stairs not the lift, make multiple trips up & down my stairs when I could do it in one or two trips, etc. but that’s it.
Yes, I know there are lots of benefits to exercising and with all things you have to do what is best for you.
PS - Glad you’ve found a therapist.