What Causes Discharge Of Pus While On UTI Treatment?

I had uti before one month and take oflomac 200mg for a week but the fever persists and stopped oflomac and start to take doxy for 3 days and got relief. After one week reinfected and consult urologist and start to take clavituf 625 for 20 days and then take niftas but again reinfected but no growth in culture. Again I took clavituf for 14 days and consult urologist. He stopped antibiotic and gave afdura for one month. Now after one week small quantity of pus coming out but I am totally comfort. Is there any problem and daily I will 3-4 liters of water. I did IVP Xray and US scanning but no other symptoms identified.