What Causes Soreness And Stiffness In Neck?

I'm a 19 y/o female and recently I've been fighting a fever. It's been about 2 weeks, and the fever's been on-again-off-again (I'll get it every other-dayish). I'm taking a bunch of vitamin C, zinc, B-vitamins, and the like, but today my throat started to hurt and I coughed up a bit of brown mucus--not much though. My shoulders are sore and I can't tell if my neck is just being sore or starting to get stiff. Also, I have a lightly sweet taste in my mouth, but that just started yesterday. I'll admit I over-indulged during the holidays and I had a lot of sugary foods...definitely came back and bit me.