it sounds like it could be a whole range of things, from kidney problems, to perhaps another UTI (though i'm shaky on their first diagnosis, but hey i'm not a doctor so i can't really contest it) or it could be appendicitis, this time around. i'm glad you've made an appointment and, to the person above - MAKE ONE, now. if you have appendicitis and it goes untreated, your appendix could perforate ("explode") leading to several icky circumstances. OR it could block your intestines OR it could cause sepsis. if it's not appendicitis, still go to your GP. there is never any sense in 'not making a fuss'.
anyway.. back to the OP - i must say that if you have already had a UTI, perhaps because of certain behaviours (not peeing before&after sex, non-cotton underwear, etc), it's more likely that you'll get another one.