I am experiencing lower abdominal pain when i sneeze, whilst sitting and laying down. ?

Maybe muscle: There can be a lot of reasons. It could be the abdominal muscle, it could be an internal abdominal problem, it could be a hernia. You need to discuss this with your physician

Muscle spasm : You probably have a muscle spasm and it should improve with time. If you have been coughing for a while you can strain these muscles and have pain when you cough and sneeze. These problems are usually superficial in the abdominal wall and not deep. If it is deeper see your primary care doctor sooner then later. Good luck and feel better.

Varies: Multiple possibilities, consider being seen for accurate diagnosis. When you sneeze, that increases your abdominal pressure, which can make many abdominal conditions more symptomatic, so it is kind of a non specific complaint. A hernia is just one example of many conditions that can become more symptomatic when intra abdominal pressure is increased.

Go: To a physician or urgent care office for examination. Any constipation or dysuria?