Just some random thoughts:
It is spring, after all -- and there are lots of things starting to grow that you might be allergic to. For example, I am particularly sensitive to grass and grass pollen, so while I love having the windows open and the fresh air coming in, my head is stuffed up, I'm sneezing and coughing, and while I don't have a fever -- I'm sure if I went to a doctor he'd find congestion, fluid in my ears, all the "usual" signs of respiratory problems. This happens to me whenever grass is growing and/or is being freshly cut, and blowing around. I'm also sensitive to oak pollen -- same problem, this time of year, and again in late fall. Could there be something new in your environment (like for me, the fresh growing grass) that's causing your problems?
Then -- if there is nothing new, if indeed you don't have an infection or cold (not all sinus infections come with fever/pain/ etc....but can simply be a "stuffy head")...
then perhaps you're experiencing what is called the "MS hug" -- a feeling of squeezing in, pressure, around your torso (most often from waist to top of chest), a feeling that your "insides" are being squeezed. Often people feel shortness of breath, even have thought perhaps they're having a heart attack...but it's a sensory thing, another one of those really annoying MS things.
It's good that the pharmacist "caught" the issue of your penicillin sensitivity, and is trying to change the prescription.
An anxiety attack is usually a big more dramatic...anxiety-producing...the adrenalin surges through your body, you feel like you want to flee the scene. It doesn't much sound like that is what is happening for you. But then,
...I am not a doctor, nor health professional, and don't pretend to be one, here.....