Lower back ache that radiates just above both butt cheeks and around to below abdomen above pelvic. worsens when i bend over.. fast onset no injury?

Back pain: Any radiating back pain may be a sign for a nerve involvement. I would see an orthopedic who specializes in back disorders.

Low back pain: Pain that only radiates unto the buttocks can never be from a pinched nerve. In your case it is likely that a disc is causing the pain. That pain also causes muscle spasms adding to the pain. It may have started in the past and got aggravated recently. Avoid prolonged sitting. Use a pillow behind your lower back. Avoid lifting heavy objects at least for a year. Most discs heal by themselves.