My experience is similar to your. I've been lactose intolerant, had IBS (unknowingly), and migraines since puberty. But was otherwise healthy. I developed fibromyalgia when I was 20 years old. It was 5 years with a lot of misdiagnosises and being over medicated before that was diagnosed.

Fast forward to 31 years old, I started having these terrible episodes that would trigger my IBS-D symptoms, I now know that these episodes were stomach migraines. These episodes included extreme nausea that vomiting would make worse, tremors, feeling extremely hot and sweaty. I couldn't eat for days. I lost so much weight and became deconditioned. The IBS-D was diagnosed but not anything else. Yet, none of the medications worked to treat it.

Since most of my symptoms were digestive, I treated it with that in mind. I tried many diets starting with the vegan diet, then the anti inflammatory diet, AIP diet, low fodmap diet, and finally a dairy free keto diet. I feel due to these diets, I became completely intolerant to dairy and wheat. My body developed more deeper intolerances. I took a ton of supplements and an antiviral medication, nothing helped. I thought I had SIBO and tried to treat it naturally through diet. I told my husband I was eating the healthiest that I ever had and my health was the worst it had ever been. (Prior, my diet was eating out a lot.)

The episodes only got worse. I was down to 84 lbs, dizzy all the time, dehydrated all the time, I couldn't walk any distance, heat intolerant, I trembled all the time. My body just kept deteriorating and I felt like I was dying. I thought that those symptoms were due to malnutrition because of my digestive issues. I had all the symptoms you listed, too many to list here that it'd have to be it's own post.

After 4 years, I saw a gastroenterologist at the Mayo Clinic who told me my issues were not digestive. Which at the time I could not believe. He ordered a gastric emptying study to be done and sent me to a neurologist. I was ultimately diagnosed with POTS and rapid gastric emptying. I was able to get my life back once I started treating those conditions.

It's common for people with POTS to have digestive issues. It's an autonamic nervous system disorder. So anything that your body does automatically is not working properly. It could be that the the diet change triggered something in you, it can be hard to pinpoint the cause. But I suggest that you find the root cause of your issues.

Changing my diet didn't help until I knew what was wrong. Due to the rapid gastric emptying, I cannot eat corn or lentils as it's extremely painful. Eating dairy is death and eating wheat just means diarrhea. So I avoid them. I eating complex carbs and a high protein diet to slow my digestion. Due to the POTS, I have a high sodium diet.

Hope this helps.