Why do doctors have to press your stomach? And why does it hurt so much?

Everytime i go to the doctor, they always press on my stomach, whether im sick or if im just going for a checkup. Do they HAVE to do this? i mean i understand if im going to the doctor for a stomachache but lets say that i go to the doctor fot an earache, is it absolutely necessary for them to still check my stomach? And also, is it normal for it to hurt when a doctor presses on your stomach. Thats the only reason i hate it so much is because everytime a doctor presses down, i feel pain, even if im perfectly fine and the doctor says nothings wrong with my stomach. Its not a severe pain but its sort of sharp but not too sharp. Also, i think the pain is just a tiny bit more intense on the lower part of my abdomen, but not by much, Is this normal?