Can an ultrasound be used to diagnose weak pelvic floor? will a hernia look different from any kind of prolapse due to pelvic floor weakness on ultrasound?

Not completely: A dynamic examination (with the pt pushing, valsalva or kagel maneuvers) is required. Urinary incontinence DX requires urodynamic study of bladder contraction, bladder neck relaxation. Seek advice from a urologist or a urogynecologist.

Hernia different: Typically a cat scan will be used to image a hernia but a good ultrasound tech may be able to capture a hernia with forced intraabdominal pressure manuevers. Pelvic floor laxity or weakness or prolapse can be seen on physical examination.

Yes: One of the best imaging modalities for pelvic floor defects is 3d/4d ultrasound. However, the technique, trained personal and equipment are not available in every community.