Hi Astrid - Sorry you're having such a hard time! I would suggest you look into Celiac disease as the possible source of your malabsorption. There is a Celiac forum here at HW also, and, of course, lots of information on the internet.
Most doctors are not familiar with it, and fail to diagnose it. There are now gene tests that can be done to help pinpoint the problem - but like other autoimmune problems, it's not easy to diagnose, even with the gene test.
Celiac is an autoimmune disease in itself - if you have it you cannot process gluten (wheat, barley or rye), in your diet, and until gluten consumption is stopped, damage to the small intestine will continue and is what causes the malabsorption - which of course, causes other problems due to the deficiencies that arise.
I've was dx'd about a year and a half ago, and gluten free since then. It has not solved all my problems - but I have had some good improvement. Good luck and hang in there!
I hope the specialist you'll be seeing will have some answers for you.
Take care - Lucy