To say "I have a stomachache" in Engpsh, you can say "I have a stomachache" or "My stomach hurts." For example:
Person 1: "Are you feepng okay?"
Person 2: "No, I have a stomachache."
Alternatively, you could also say:
Person 1: "Is something wrong?"
Person 2: "Yes, my stomach hurts."
If you want to be more specific, you can also describe the location of the pain or the intensity. For example:
"I have a sharp pain in my lower stomach."
"I have a dull ache in my upper ah3men."
It's always a good idea to see a doctor if you have persistent or severe stomach pain, or if you are experiencing other symptoms that are concerning.