Reasons for the pimples on my butt?

So I am 19 and sexually active. A few weeks ago I had symptoms of a yeast infection and bought Monistat 7 to clear it up. I also had one pimple on my butt at the time. After I had finished the medicine I felt better and figured that was the problem. Until recently when I have been getting a burning feeling down there once again. I have also gotten three more pimples on my butt. My boyfriend says he is positive that he doesn't have any STD's because he was tested not long ago. I have not had any of these symptoms until him. I'm not sure if this is just another yeast infection or if there is really something wrong with me. I'm afraid to go the the doctor because my parents don't know that I'm sexually active. What should I do?