IF and a messed up metabolism

I’m 46, SW 241 CW 225 GW 175, 2.5 years post head injury and have several chronic illnesses- as well as hormonal imbalances. Am cleared by Dr and nutritionist to do IF. Lost first 10 pounds over 1 months with CICO. Then 3 month stall. The shock approach seems to be the only way my body will lose. A decade ago I ran 1/2 marathons for fun and was fit and healthy- utilizing KETO. So I know the ropes to a decent degree. But my body is literally a mystery. Nothing works like it should. I am trying to gentle but am pissed about being fat. I have been doing IF for 5 weeks and lost 6 pounds in 3 weeks- mostly 16:8. Have extended fasting window to 20-22 hours with no issues but then no more weight loss. I dirty fast with NUUN (stevia) electrolytes due to having POTS- occasionally LMNT unflavored. Exercise is recumbent and HR based due to POTS and CFS- cannot push hard. Since I’ve extended the fasting window I am not losing/ but also not hungry. TDEE is 2000-2400 depending on exercise and I work to get 1200 calories in 2-3 hours. Guessing I’m not eating enough but stumped on how to work with my metabolism. Head trauma is likely an issue to- as most people who have mTBI struggle with weight gain. Any input would be REALLY appreciated!