Losing Weight. Medical Test Fine. Feeling Headache, Tired, Nausea And Appetite. How To Maintain Health?

Question : Hello, my sister is losing weight unintentionally, she is struggling to keep the weight on. She is weighing on 38kgs and is 24yrs old!!! We have been to numerous doctors and Physicians per the past few week,, and TWICE to the ER, they have done CBC, Thyroid Function, Cortisol, Liver Kidney. but all is fine as they say... She is FORCE FEEDING herself just so that she does not drop any further in weight. She has CONSTANT Headaches and IS UNABLE TO WORK anymore, as since this weight loss began, she has become CHRONICALLY TIRED, she used to shop for hours and walk, but now she can't even have enough strength to dress herself. I AM SCARED, doctors just keep ignoring us. I will show you pictures of how she look 3 months ago, she was lively, look healthy etc...now she is looking gaunt and it is worrying us all. When the weight was dropping off, she ATE a lot even had MRP's in-between, but it just fell off. Now she has chronic nausea and no appetite, but still forces food down, and has to takes anti nausea tablets daily....The doctors are not helping us.....how can a lively 24yr old just become almost bedridden and loose so much weight. WE ARE 300% sure she is not bulimic or Anorexic..GUARANTEED. She complains of acid reflux and mucous in the throat and nose, as well as a nausea and discomfort radiating from her central abdomen(just below the ribcage, in thee center of the torso). She also has severe hard like muscles on her shiulders as if it is knotted, her right sholder seems to be in spasm?? Also she has been comaning of feeling feverish, And that her arms are weak. For that past couple months she seems to have knee troubles, and can finds it painful to walk down stairs etc. She has had a negative XXXXXXX to rule out Lupus. Please help as it it now two months and she is no longer the healthy sister i knew... Please help us.....From a concerned brother. PS we are in Johannesburg South Africa

Thank you kindly for the response Dr. I had demanded this to the Dr when I took her to the ER a month ago. The Dr responded that she did not have malabsorbtion as her blood tests showed normal levels of fats and proteins etc. however one must realise that at this time she had been consuming a diet that was her 3 meals per day including MRPs like Ensure ans Lifegain inbetween, so her food consumtion was much higher, so i was thinking that if she returned to a normal diet, perhaps the blood and fats in the blood would decreaze below normal... I wAs ignored. I recommened to the Dr that that they shoulc check for things like celiac or chrons and they did an IGn test and it came up just above normal i.e 108 and the spec was 1-100. I was also thinking things like a parasite like tapeworm etc but the blood eonsophils were normal and the Dr said they would be raised if a parasite was present. She as of now has an appetite that comes and goes due to the nausea and headaches but she is still forcing herself to eat to keep on some weight. Theblood procfile as of recent included tests for iron, ferratin, b12, fasting glucose all were normal except a high normal for iron. She remains at hime wasting away and does not want tovisit drs anymore as she says they are failing her. Any direction forward would be appreciated:
Ps just to add to my second response to you above the Dr also performed a C- reactive protein and erythrocyte sedimentation rate and both were normal actually very very low, does this exclude a diagnosis of malignancy?