I have most of the symptoms of sarcoidosis such as fatigue, erythema nodosum, shortness of breath, but the test i took for sarcoidosis came back negative. why the erythema and other symptoms?

Many causes!: Erythema nodosum may occur as an isolated condition or in association with other conditions.Conditions that are associated with erythema nodosum include medications (sulfa-related drugs, birth control pills, and estrogens), strep throat cat scratch disease, fungal diseases, infectious mononucleosis, sarcoidosis, behcet's disease, inflammatory bowel diseases (crohn's disease and ulcerative colitis).

Other diagnosis: The results of the test could be a false negative. More commonly, another disease is to blame. Check out the following website: http://www.Ncbi.Nlm.Nih.Gov/pubmedhealth/pmh0001884/. You need to see a good internist that can complete the workup and determine the diagnosis.