Sharp, shooting pain in both sides at once?

Sarah
Its a little below my wait. And I can feel the pain move from somewhere in my abdomen to both of my sides at the same time. I've googled it many different ways, and all I can come up with is my uterus stretching. However, I took a pregnancy test and it says negative. 
​My period is due tomorrow, but these are not normal cramps or cramps at all. 
​Thanks in advance for any help! If there's anything you know of that could be causing this please let me know.