"I have bowel issues, my legs/arms can sometimes feel heavy/odd, and sometimes I have pain [more like soreness] in my lower back/hips when I've eaten but am constipated." You literally have the exact same problems I'm struggling with that no one can find an explanation for. About 2 years ago I had troubles with gagging all the time and they diagnosed a small hiatal hernia, for that I took PPIs then about a year ago in May 2019 I noticed a sudden change in stool it took on every form or colour imaginable and I had a lot of pain in my epigastric area. I did multiple blood tests which only showed elevated levels of bilirubin but still within non dangerous levels. I did CT scan of abdomen and thorax which were both normal. But yea for a year now I am super fatigued all the time, my legs and upper arms can feel really strange (like a mix of crawling, heaviness, weakness, creepy) and I also feel weird/sore around my kidneys in the back but I can also feel it on 2 points from the front of my body (where my kidneys would be located).

I do not think Restless legs was the correct diagnosis unfortunately. Your case seems so similar to mine and I believe it is something in the gut. Just yesterday by chance I discovered that after oversaturating myself with vitamin C, which leads to watery diarrhea made me feel temporarily a lot better. I'm theorizing that there could be a bacteria or fungus in my gut that releases toxins that produce these symptoms in me. And the watery diarrhea acted as a kind of gut cleanse for a few hours which washed away the toxins for a period of a few hours.

You could try the experiment yourself if you have symptoms, if you experience the same relief it could point us both in the right direction. I drank half a glass of water mixed with a teaspoon of ascorbic soda every half hour until I have to rush to the toilet (Your guts will rumble a lot). It usually takes like 4 glasses and you'll end up an hour on the toilet.