Sep 8, - Signs and symptoms of mononucleosis may include: Fatigue. Sore throat, perhaps misdiagnosed as strep throat, that doesn't get better after treatment with antibiotics. Fever. Swollen lymph nodes in your neck and armpits. Swollen tonsils. Headache. Skin rash. Soft, swollen spleen. Sep 11, - When older people get mono, they usually have slightly different symptoms than if they were much younger, which can be confusing for the.