Went to er w/ chest pain, sinus pressure, lower back pain and total body weakness. this is my last day of zpack and prednisone and i don't feel better?

Viral: This might be then a viral infection and hence antibiotics will not help. Rest, hydrate and try a sinus rinse kit which you can buy over the counter such as Neil Sinus Rinse, or net pot.

Viral infections: Cause most illnesses, and your symptoms are consistent with a flu-like viral syndrome. Symptoms can last 7-10 days. If you are short of breath, wheezing, or your chest pain is persistent or worsening, see your physician for a recheck. Otherwise, fluids, probiotics, rest, and anti-inflammatory medication such as Ibuprofen should see you better within another week. Best wishes