Not Responding to Medications

I am a 20 year old female in college. I got sick very quickly a week ago.  My boyfriend was ill for a day or so, and then I became very ill and have yet to recover.  My symptoms are as such,  I have a lot of sinus congestion, post nasal drip, sore throat, fatigue, and sinus pain.  I was treated with a zithromax - pack? I think thats what it is called.  It did not work though, and I now am experiencing severe neck and back stiffness. It is really painful and has persisted for three days now. I went back to my doctor when the antibiotic didn't work, and they informed me I just needed to take a stronger dose, but after feeling worse from taking them in the first place I am worried this may not just be a sinus infection, as our university health services are notoriously shoddy.  I have never struggled this much with a sinus infection before and my neck and back pain is intense and is making it hard to go through the day, along with the sinus issues.

In looking on my own some sites stated it could be mono, or even meningitis.  Obviously neither of those results is really happy, and I am not sure how likely they are, but this neck pain is nuts, and I am starting to have issues thinking clearly. Is this just a really bad cold or flu?

If there is any insight into what is going on with me I would sincerely appreciate it.  Even questions I should be asking my doctor about what is going on with me, or things I might be able to do to relieve this pain.

Thank you so much.