I have strange spots appearing on my bottom left butt cheek. In the last month, I took macrobid for a UTI I got. Then I took bactrim for the first spot. It was red and the size of a dime. It hurt when it was rubbed against. My doctor thought it was a spider bite but just yesterday I got another spot and it looks like the same thing. They leaked a clear substance. The first spot is now just a brown mark. But the new one is starting out just like the first one, red and painful. And there s a third brown spot in between them. I ve been having unprotected sex for the past month with the same person. I don t know whether that person is clean or not.