I have been getting stomach cramps on the lower left side for almost 12 hours. what can be the cause and how can i relief it?

Get it checked out: There can be a lot of things causing left lower abdominal pain including constipation, infection, colitis, kidney stone, bladder stone, and many more. The only way to tell is with a careful history and examination. Also some tests like x-rays, ct scans, and/or blood tests may be needed to narrow it down. 12 hours is a long time. Go see a doctor and get it checked out.