I would not advice ingesting castor oil however you can make castor oil packs (see tutorials on youtube) for the abdomen which may help with constipation. Hypothyroidism usually causes constipation because of the underactive stomach so typically something that would work much better for constipation would be increasing fiber (chia and flax), increasing water consumptions and using Betaine HCL (if needed) to improve stomach function. Moringa tea can help move the bowels a bit if you’re drinking consistently.
Corn are pure starch so any corn products can cause weight gain as it converts to sugar in the body which usually gets stored as fat.