My Daughter Is 17 And Very Active. She Started Feeling

My daughter is 17 and very active. She started feeling sick several weeks before thanksgiving. Doctor said sinus infection and gave her ZPak, which didn't help. She had a bad cough and head congestion and headache. A week and a half later she had the same symptoms only now her ear hurt as well. Took her back and they said ear was red and some fluid. Started another antibiotic, which didn't do anything. Took her back again and started a third antibiotic. Still not better but ear was not red and no fluid. Started her on a steroid last week on Thursday. Friday she started in with severe headache and sharp stomach pains. She is not able to participate in any activities or be in school. I requested blood work, so today they tested for mono and strep (both came back negative). They are also checking her blood count and I don't have those results back yet. My younger daughter was having the same symptoms and she missed 2 weeks of school. She is able to go to school but is still not feeling good. They did an Xray of her head and stomach and said she had a lot of stool, even though she had been going every day. They never came up with a diagnoses for my younger daughter