I ve few throat ulcers, and soreness and redness in throat, this occurred on 5th day after onset of use of suprax (cefixime) for uti, what may be the cause?

Virus? Herpes?: Probably urelated to Suprax (cefixime). Sore throat with ulcers sounds like a viral infection -- several possibilities, but one if them is new herpes. Was your UTI confirmed? Did those symptoms clear up? I'm wondering if you may have had sexual exposure with a new HSV infection both oral and genital. But of course only if at risk of STD. See MD ASAP, sooner the better for accurate diagnosis and effective Rx.