It could be an STD, but don't assume that until a qualified physician runs tests. Some common urinary tract infections can get out of control and become life-threatening if left untreated for more than a few days. (That's why some doctors will start you on a broad-spectrum antibiotic even before test results are available.) You will probably know that the antibiotic is doing its job within a day or less, but be sure to finish the entire prescription.
The doctor may prescribe a urinary analgesic to relieve your discomfort. "Pyridium" will turn your pee a sickly orange color, but that's normal.
Until you can get to a doctor, drink as much cranberry juice as you can. Read the labels on the bottles in your supermarket and buy the ones with high percentages of actual cranberry juice, rather than the "blends" and "cocktails" that are mostly some other fruit juice. The topic is under debate but there is some credible scientific evidence that cranberry juice can slow the advance of UTI's, even though it doesn't seem to cure one that you've already acquired. (Seed a search engine with "honeymoon cystitis" for more information.)
