27 y/o female with 4 days history of fever, night sweats, headache, generalized painful lymphadenopathy, fatigue, elevated liver enzymes? Mono neg

Guess u want DDx. Ddx=differential diagnosis involves the most important, under-used, under-appreciated, under-paid, complex tool a physician has: a trained/experienced mind, fueled by a good heart, driven by a mission to help others. Excellent history (listen!), careful physical exam leads to the answer, or at least to next step.? Viral illness? Drug reax. Rest, fluids, wait 2 wks; persists? Work up further.
Other infections. Check HIV CMV also consider fungal infections if you are in one such area in the country. If there is an easily assessable lymph node get a core bx, fna is inadequate.
Viral Vs lymphoma. Possibly viral illness; other differential is lymphoma eventhough duration is short. Other differential depending on history - hiv, tb.
Bacterial infections. Looks acute- any associated pharyngitis? To look for other rare causes TB / lymphomas.
Viral. Consider adenovirus, enterovirus, influenza, and hepatitis a, b, and c. Follow liver enzymes and check pt and bili. Recommend no acetaminophen. Monitor to ensure liver damage does not escalate to failure. Consult local transplant center if pt develops liver failure.