SIBO and/or candida are just normal when you are hypothyroid. Do not try to fix those if you haven't resolved the hypothyroidism!
You are likely to cause significant damage in the attempt. Killing bacteria releases significant toxins and they will regrow in like a week. If they don't they are gonna be replaced by even worse bacteria. No way to win.
To fix hypothyroidism change your diet to mostly milk and fruit. Takes about 2 years, don't be impatient. Your gut will probably improve by itself afterwards, if not then you can experiment. NDT or synthetic thyroid are just for managing symptoms.
Anxiety: Reduce your serotonin levels.
To do that:
L-Theanine - Increases GABA and Dopamine levels in the brain, Dopamine reduces Serotonin, L-Glycine - Affects your nervous system so that it doesn't signal Serotonin increase. L-Taurine - Lowers serotonin release directly. Ginger - Lowers the synthesis of serotonin.In combination incredibly potent. They all dissolve in hot water, steep some ginger in hot water and add like half a tea spoon Theanine, half a tea spoon Taurine and one tea spoon of Glycine. Sugar to taste. Anxiety should go away basically instantly.