Sir, My Son Is 21 Months Old. Recently He Got

Sir,
My son is 21 months old. Recently he got UTI treatment with ZIFI 100. After using that his fever and other problem subsidised but his appetite has become very low. He is not eating anything only drinking water and breastfeed and very little eating. It has been 1 week now.

Otherwise he is active but very adamant he has become and irritative. He shouts and cry for small things.

Please suggest what to do