I have a pinched siatica nerve. it came out of no where. could it be a sign of pregnancy? if not then why?

No: Sciatica is not a specific sign of pregnancy. However, during pregnancy some women may develop sciatica due to changes in the body mechanics and perhaps stretch on the nerve fibers in the pelvis. Otherwise, multiple factors may be the basis including but not limited to herniated discs, bone spurs, nerve inflammation and benign tumors. Persistent symptoms would require evaluation by consultant.

Are U Pregnant?: If you're not pregnant, sounds like you have a pinched nerve in your back. Can take up to 6 months to go away on its own. I would suggest seeing a pain/spine specialist to evaluate you further to evaluate what level and what can be done to treat you. There are interventional treatments besides medications and surgeries that might reduce or eliminate the pain altogether.