I have lower back pain sometimes. My period is late, but during the time it was supposed to come, I had constant nausea, bowel movement changes, frequent urination, trouble fully emptying my bladder, and a lot of gas. It seems as thought the symptoms are worst at night when I'm doing less movement. I took multiple pregnancy tests, all at different times and they were negative. Its almost 15 days after the day my period was supposed to start and I still get the symptoms, but they are off and on. I feel pressure and discomfort on my pelvis constantly.