Apart from hernia what can cause major pain in the groun and sometimes down the thigh?

Inguinal strain, or : The so-called "sports hernia", or less likely, from adenopathy, aneurism of the femoral artery, orthopedic conditions of the hip joint, arthritis, trauma... Hernia is the most common and may be symptomatic even when too small to feel on exam. Suggest an evaluation by a surgeon.

Tendons: Adductor tendonitis is a leg muscle that can cause pain that mimicks hernia pain. This is diagnosed with an mri, but a good physical exam is in order first to make sure its not a hernia.