My Son Is 27 Months Old. Recently 10 Days Back

My son is 27 months old. Recently 10 days back he had fever accompanied with swollen eyes.also he had cold and a little chest congestion.
He was prescribed antibiotics and medicines for cold.
The fever subsided after 4 days but the swelling remained.
Then we approached a nephrologist who took his urine blood and a ultrasound.
He is diagnosed with nephritis.he is been given omnacortil(15mg) along with lasilactone tabs.
I started the medicines from yesterday. But he is become very irritable and fussy and cries a lot over anything.his doctor says it is not due to the medicines.then what might be the reason.
I am really worried.also the side effects of omnacortil are really huge.
Please guide