Here is the antibiotic rule 101--- never stop the antibiotics midway. You have to take the full course even if symptoms resolve. Even if a dipstick says it is gone. If it is prescribed for 7 days, you take all doses for those 7 days. Here is why. Bacteria is SMART. You half treat it with only a half course of antibiotics . . . that bacteria probably is still there in undetectable amounts and it starts to morph and change so that the antibiotics become ineffective. This is why we have drug resistance to antibiotics. It's a scary thing and at some point, we will run out of options to treat infections because of it. Hopefully not in our life time but antibiotics that were once very effective are now useless because of improper use of them and bacteria growing resistant. That's my speech. ha ha. But it's truth.
Okay, so let's get back to your question. typically, I do not condone just treating oneself with left over medication. Two reasons--- one we aren't doctors and shouldn't diagnose ourselves and if something goes wrong, we have no medical record of what is going on and two, you don't have enough pills for a full course of therapy going back to that ability to treat this properly.
However, UTI's hurt like a son of a gun. And I would not make any woman suffer through that. If you want to START treating before you go to a doctor, I get it. But you MUST call your doctor, tell them and get the remainder of the script filled. Because otherwise, you're going to have recurrent UTI's just like you do this time and eventually, no options to treat them. :>(( good luck