My muscles feel sore and weak after taking methlypredisone/amoxicillin for chornic sinusitis.my blood work/urine came back fine, and stoped taking the medication about 2 days ago, but still feel weak/ sore. cause of concern?

Fatigue after symptoms described may indicate COVID-19, so obtain a PCR test for COVID-19 and quarantine x10 days if positive, and if respiratory symptoms occur, go to an emergency room for evaluation.

It doesn't necessarily have to be a Covid infection. Post infectious fatigue after any infection is quite common. As an example, it is not unusual to take a month for fatigue to completely resolve after a bout of influenza or bacterial pneumonia.