Remember that routine bloodwork and x-rays can't tell you that you're perfectly healthy, they can only tell you that there were no obvious health problems (I learned this as a result of mysterious health issues that turned out to be fibromyalgia and autoimmune disease - but most of the routine tests were perfectly normal. It took a lot of persistance on my part and on my doctors' to discover the root issues).
I do think that fat, protein, salt, and/or calorie levels are the likeliest culprits (either one or several of them). You can start experimenting to see what helps.
More protein doesn't mean you have to return to meat, and nor does it mean that you need to follow a low-carb diet. For some reason, moderate-carb diets don't get much attention. I have to cut carbs significantly, but I don't feel well on a very low-carb diet. In the past, I always thought this meant that low-carb diets were bad AND (my bigger mistake) instead of choosing a moderately low or medium-level carb diet I would return to a very high-carb diet. I never tried "the middle."
I'm still learning what the ideal carb-level is for me, but I've definitely learned that it isn't very low-carb, and it isn't very-high carb.
Your protein, fat and calorie levels do seem to be quite low from what you've described. so you may literally just need to eat a little more. Maybe just eating more will help, or maybe you'll have to pinpoint what you're missing. You can try to do it on your own, but I'd really recommend consulting a dietitian.
Some people don't do well on a strict vegetarian diet, even when they do get adequate protein and vitamins. However you are eating some animal protein (the eggs and dairy), but you're eating a very low proportion of protein.
Sodium level still could be an issue, even if your blood levels of sodium were normal. Although I'd consider sodium only after exploring the other possibilities.
Because this is a pretty serious health issue, I wouldn't spend a lot of time experimenting on your own (unless you see dramatic improvement after upping your fat, calories and/or protein).
Regardless, I would also recommend seeing a dietitian (I'd recommend making sure the person has credentials. In the USA, anyone can call themselves a nutritionist even without any education at all. However, a dietician needs to be certified, meeting specific educational and experiential requirements and must pass the qualifying exam and may even need to meet continuing education requirements).
Physicians (at least in the US) don't get much if any nutrition education, in the course of earning their degree. So you may not find much help from the medical community.
I don't know if this is as true in Greece, but it's something to check up on. Make sure that the "expert" you consult really is an expert.
If it persists and doesn't respond rapidly to diet changes, you might consider seeing an endocrinologist because they would be familiar with hormonal and other endocrine problems and issues like diabetes, hypoglycemia, reactive hypoglycemia, thyroid and adrenal conditions....
|
) what many others are saying above. I would guess your fat/protein levels are too low. Some people can pull off high carb/low fat and protein diets but not everyone. 
