Unless you are in major pain there is no need for the ER, drink some craberry juice 8oz a day( it nutralizes things) and just call your dr Monday morning. They will most likely prescribe something via phone. You can't leave it untreated but it's nothing to panic over.
Please don't waste your money... cranberry juice and make sure you get 8 glasses of water day and don't use any medication before you speak to your doctor.
I would wait... but, your Dr takes a pee sample every drs apt to check for uti, so if you had one recently then you would have already known. Then again I'm not a Dr, best thing to do is to drink plenty of water, you should be drinking 8 - 8oz of water every day. As long as you are not in pain it will be fine just to wait until your apt.