4year old uti now a skin rash

[Inneedofaholiday2017]

Diagnosed with a uti yesterday and given antibiotics - she's had 3 doses and I'm not sure she's shown much improvement and thus evening she's come up in an itchy rash on her torso and legs - is this normal-unrelated to uti? Her legs were a bit itchy yesterday before she started antibiotic.
How quickly should she be feeling better? Should the antibiotics have started to work by now?

[MrsGosling71]

What antibiotic is it? My daughter had an allergic reaction to Penicillin V and came out in a rash. The Drs put her on another antibiotic. Hope your little one feels better soon.

[Inneedofaholiday2017]

Trimethoprim... sounds like I might need to go back to drs tomorrow to switch antibiotics! Thanks