What Causes Sharp Pain In Lower Abdomen Along With Flatulence?

Blessed day! Hi. I m a woman aged 25. Since yesterday, I have been having piercing pain in my lower front abdomen. I can feel the pain focus in the center but there are times that I feel it in the left side, right side & both. The most painful episode was yesterday afternoon, around 1-2hours. (A 9 on 1-10 pain scale; 10 the highest.) Then the pain became much more tolerable (varying from 2-5 on a scale). I also have grumbling feeling in my lower back and have been passing gas very often since yesterday. I feel a slight burning pain after peeing since yesterday. I haven t felt like vomitting and I think my temperature s normal. No fever. We went to the hospital but they coudn t tell what this is. I waived the pregnancy test part of the check up cause I haven t had sexual contact ever. Other than that, my urinalysis & blood tests were negative.