my 13 year old daughter has had a low grade fever from 99.4 up to 102.6 for a week now, i have taken her to the doc they said she had a UTI, then took her to the hospital three days later and they said she had a viral infection, still has a fever, lower back pains and stomach pains. They did blood work at the hospital to check kidneys but they said all was fine, What is causing this? it is ok for her to go this long with a fever