Christ if it's an abdominal aneurysm it'd be the weirdest ever presentation of it. Abdominal aneurysms are usually felt as pulsating masses within the abdomen. They don't typically become a problem until they get to be bigger than 5 cm in diameter.
Anyway, alarming diagnoses aside, it sounds like you have an abdominal diastasis although it would be very uncommon in your demographic (assuming you are a young to middle aged male with no prior abdominal surgeries). Regardless, get it checked out by your primary doctor or see a surgeon. Probably nothing emergent unless it gets incarcerated or strangulated at quick point the pain should bring you to seek medical consult.
Here's a link on diastasis: LINK