What could cause this random fever?

I started to feel fatigued and nauseas yesterday afternoon. My nausea was so severe but I didn't vomit. My husband made me an alka-seltzer drink with mineral water and lemon to combat the nausea feeling. Ever since I drank that I've felt better but the weird thing is this morning I woke up with 100.3 fever and I'm not sick with with sneezing, coughing, or sore throat. Just woke up with the fever and weakness and very slight body aches. I took ibuprofen to lower my fever and in 4 hours it got down to 98.5. Would anyone know what caused this fever? Has this happened to anyone else?