Undiagnosed Symptoms :: Nausea / Exhaustion?

I am 20 years old and it's been at least 4 years since I started experiencing these symptoms. I am unable to perform normally in life (I have been struggling to live normal life up until now, I can't just take it anymore.) I'm from Czech republic so pardon my poor language skills.

These are symptoms I experience:

1) sore/stiff muscles, stiff neck, my muscles slightly hurt me when I stretch

2) being weak, tired, exhausted, feeling fatigue/nausea - nowadays basically to the point where I don't get up from bed whole day if I don't have to, this can go on for months even (when I have holidays)

3) permanently yellow/orange-ish stool no matter what food I eat. Eating fried food sometimes makes me feel worse. I think I also often go to the toilet - once every 3 hours. Similar for water: I drink usually 3 litres a day through the day and my bladder hurts me very slightly all the time - the more I drink, the more it starts to hurt.

4) symptoms as if I had mild cold all the time - permanently stuffy nose, sweating (it goes like this - I start to feel cold but when I get into warm environment, I start to sweat)

5) visual snow, feeling dreamy (aka depersonalization/derealization)

6) generally unspecified weird/unpleasant/painful sensations across whole body

Symptoms never go away, no matter how much I rest (when I don't rest, it obviously worsens them a lot).

Cold weather feels very bad to me so symptoms probably get little worse when its fall/winter.

I have undergone mononucleosis over a year ago, but as I said, I had the symptoms even before. It's however possible that mononucleosis worsened it.

I have been to several medical places during this year including gastroenterology (stool/blood/gastroscopy, ultrasound of my guts), oncology (blood test, it's known that I have 2 genes that make me more prone to cancer - family origin), immunology (blood test) and infections department (blood test).

All the results were negative except the few that had border values - smooth muscle antibody and something that indicated that I must have undergone lyme disease some time ago. (and the results from oncology)

I tried taking vitamins, magnesium (with B6 and B12 vitamins or so) and supplement that supports liver function (contains choline and few other things). It does not do anything.

As of the fact that I must have undergone lyme disease some time ago, I was prescribed antibiotics for 15 days, I have been taking them for 7 days now but I don't feel any better. Well they make me feel somewhat fresher, but all  my symptoms persist.

I tried I think 2 or 3 kinds of probiotics but it did not help. I was also prescribed pills at gastroenterology to slower indigestion process (or something) 6 months ago, but I haven't started taking them yet.