Lower back pain, constipation, gas, frequent urination, and all tests were negative for infection. what could this be?

Needs investigation: Complex symptoms such as these need a full history and investigations such as a colonoscopy or MRI to rule out sinister causes such as malignancy. It is prudent that you see a specialist if your family doctor is unable to determine the cause of your symptoms

Uncertain: It could be the constipation, but there can be other issues that can cause constipation and some of the symptoms. This could be a muscular problem, pulled muscle, tendon, or even a bursitis. You need an evaluation to help clarify your symptoms