Sorry to hear your troubles.
I will be talking supplements here, and many, since it looks like you may have multiple deficiencies.
It is possible to develop them if the food is grown on poor soils (almost always the case now; this is why animal growers always supplement the cattle with vitamins and minerals in the western world; when we stop eating animal product we suddenly drop that transferred through the animal supplementation; it is best in my opinion to avoid the re-introduction of animal product, but to supplement as a regular practice -- until be get to produce our own plants on a rich soil ....)
I am not sure how Drs can rule out deficiencies, since there are many and some are obvious (given the mineral, eg.g. magnesium, is rather intra-cellular, so blood test is unrealiable).
You can try few.
B-complex for nerves and brain function, will also make muscles work better due to better innervation. Zinc, Glucosamine, Shark cartilage (I know it is not vegan/vegetarian, but if you need it - you need it) or better Great lakes hydrolyzed gelatin (there is grass feed too - the green one), Copper, and increase avocados - for joints.
Magnesium citrate, potassium bicarbonate (don't do more than a 1/2 tsp in the beginning) for everything, together with Sea Salt , Lugols' drops 2 incresed to 10, by a drop a week, a day, Coral calcium, 2 tbsp a day of flax seed - freshly ground - for everything.
CoQ 10, acytl-L carnitine, Branch chain amino acids, creatine, Tangy Tangerine 2.0 (good taste and combines many supps - you can start with only that one, and it is not cheap) for energy.
I know it is lot, but use your intuition where to start and vary the supps over time, seeing in the process which ones help you best. It is not cheap, you can try Swanson - they have good and not soo good brands, but you can get good prices. Also the Brand NOW is affordable there.
Let us know how you are doing.