Hmm - if you do feel a bit better when you cut out gluten, a few other things that might be worth trying – one at a time:
a) try going absolutely, totally, obsessively gluten-free, in case you are sensitive enough to gluten that even tiny amounts of it are enough to keep your fatigue going. The most definitely-no-gluten-at-all-or-anything-that-might-act-like-gluten list of things to avoid I've found is the glutenfreesociety.org’s guideline for avoiding gluten. Their list even includes all the weird and wonderful things that you'd never think about containing gluten, like the glue on envelope flaps, lipstick, and even prescription medication. A gluten-intolerant friend of mine couldn't figure out why she was suddenly reacting to her diabetes medication, so her pharmacist phoned the manufacturer and sure enough, the company had started putting a wheat-derived starch in the tablets. I was also fascinated to see that GFS also says to eliminate corn, not because it contains actual gluten but because it contains gluten-like substances that can cause a similar reaction to gluten in some people - I hadn't known that and find it interesting because I react badly to corn and things made out of corn like corn starch, although corn doesn't cause my joints to flare the way gluten does. If you feel better following GFS’s very strict diet, then you can try adding back the gluten-free foods you miss most, one at a time, such as corn or rice (preferably rice grown in low-arsenic areas). If you search "gluten free vegan diet" you'll find some great recipe ideas you can tweak to meet the strict GFS criteria. Given your ferritin level and the fact that you’re eating a vegan diet, I wouldn’t worry much about avoiding iron-containing plant foods – if you want to keep your iron absorption low, just don’t take vitamin C with them (vitamin C increases iron absorption from plant foods) and do drink tea with them (tea reduces iron absorption.)
b) cut out soy. Some people get really fatigued when they eat soy or drink soy beverages, possibly because soy affects thyroid function, or possibly because it contains plant estrogens (aka phytoestrogens) that stop our own human estrogen from working, or possibly both. If you feel better off all soy, you could then try adding back only traditionally fermented soy sauce (gluten-free of course), tempeh, natto, and miso. I really miss edamame, but baby green chickpeas (garbanzo beans) are pretty close! A substitute for commercial non-dairy milks that I like – blend full fat coconut milk and cashews until smooth, then add in some calcium carbonate (old trick from England during WWII for getting calcium without dairy, when they used calcium carbonate to fortify bread), and dilute with water to the desired consistency. Let me know if you want the actual recipe . . .
c) cut out nightshades (tomatoes, tomatillos, bell peppers including paprika and cayenne pepper, eggplants, potatoes, I think goji berries, and tobacco – which can be used as a culinary herb to give a peppery taste). I use grated zucchini as a substitute for tomato sauce. Pepper (as in white or black pepper berries that you grind up) is fine because it’s not bell peppers. Sweet potatoes and taro are good potato replacements. Crunchy colourful bell pepper replacements in salads can include radishes, apple slices, red cabbage, red onions, carrots (especially those neat multi-coloured heritage carrots you can sometimes find) and there are lots of colourful berries – blueberries, raspberries, cherries (especially good for muscle and joint pain), cranberries, etc. etc. Nasturtium flowers and buds are edible and give a lovely peppery taste to salads.
d) you are very likely already avoiding glyphosate, given the increasing speculation that glyphosate (Roundup used to kill weeds and/or desiccate food plants that are genetically modified to be resistant to glyphosate) may contribute to chronic fatigue, possibly because it changes the nutrient levels in the food plants, possibly because it suppresses the friendly bacteria in our guts that make nutrients for us, possibly because it messes with our hormones, or who knows what. More research really needs to be done, but each of us can carry out a personal experiment to see if there’s any difference in our fatigue when we avoid glyphosate as much as possible.
I hope some of this is helpful -