@marciakeren I understand how your experiences could make you nervous about eating foods. I was wondering if there could be other contributing factors that could cause constipation like perhaps other prescription drugs or antibiotics? It may be worth talking to your pharmacist for information. Have you been on antibiotics that would be killing off your normal healthy gut bacteria? You can re-establish beneficial gut bacteria with supplements or foods like yogurt. These would be questions to ask your doctor as to what is right in your situation. Water consumption is also important because your body will reabsorb it from the colon if you are dehydrated. Your body needs water for kidney function in removing waste products from the blood stream. Ask your doctor how much you should be drinking on a daily basis, and remember caffeine is a diuretic and removes water from your body.

This is from Harvard about gut bacteria https://www.hsph.harvard.edu/nutritionsource/microbiome/

Has your thyroid function been checked? A low functioning thyroid does cause constipation and I have experienced that myself. I had Hashimoto's thyroiditis which can cause hormone levels to fluctuate and eventually the thyroid will have low levels of its normal output. I do take a prescription of natural desiccated pig thyroid and if I do not get enough, I get constipated and tired. When my dose is right, all is well.

Here is a link.
https://www.mayoclinic.org/diseases-conditions/hypothyroidism/symptoms-causes/syc-20350284
Has your doctor discussed any of these possible issues with you?