Would an ultrasound of abdomen show hernia? If you're testicles hang very low-stomach protrudes out when empty not overweight, signs of what? Age 23

Physical Exam Best. A hernia is a hole in the abdominal wall through which the inner layer of the abdominal cavity stretches thru, creating a sac. The problem with ultrasounds (or even ct scans) is that they are usually done laying down; gravity and relaxation of the abdominal wall may allow the hernia to reduce and be missed. The best exam is done standing, with and without exertion. I recommend you see a surgeon.
Yes. An ultrasound is a very good tool to detect hernias. If your concerned about your stomach protuberance go be evaluates by your md.
Unsure. If you have changes in your structure of the abdomen and testicles you need to be checked. Waiting can be very hazardous.