I just found this on the website that I'm going to list below. You really need to go RIGHT NOW!!!!! Especially since the lump is coming and going. THIS IS WHAT IT SAY>>>>>(Seek immediate medical help if you have a pulsating lump in your abdomen along with severe abdominal pain. This could be a sign of a ruptured aortic aneurysm, which is an emergency condition.)
SOME OTHER CAUSESCAN BE:
Abdominal aortic aneurysm can cause a pulsating mass around the navel.
Bladder distention (urinary bladder over-filled with fluid) can cause a firm mass in the center of the lower abdomen above the pelvic bones. In extreme cases it can reach as far up as the navel.
Cholecystitis can cause a very tender mass that is felt below the liver in the right-upper quadrant (occasionally).
Colon cancer can cause a mass almost anywhere in the abdomen.
Crohn's disease or bowel obstruction can cause many tender, sausage-shaped masses anywhere in the abdomen.
Diverticulitis can cause a mass that is usually located in the left-lower quadrant.
Gallbladder tumor can cause a tender, irregularly shaped mass in the right-upper quadrant.
Hydronephrosis (fluid-filled kidney) can cause a smooth, spongy-feeling mass in one or both sides or toward the back (flank area).
Kidney cancer can sometimes cause a mass in the abdomen.
Liver cancer can cause a firm, lumpy mass in the right upper quadrant.
Liver enlargement (hepatomegaly) can cause a firm, irregular mass below the right rib cage, or on the left side in the stomach area.
Neuroblastoma, a cancerous tumor, often found in the lower abdomen, that mainly occurs in children and infants.
Ovarian cyst can cause a smooth, rounded, rubbery mass above the pelvis in the lower abdomen.
Pancreatic abscess can cause a mass in the upper abdomen in the epigastric area.
Pancreatic pseudocyst can cause a lumpy mass in the upper abdomen in the epigastric area.
Renal cell carcinoma can cause a smooth, firm, but not tender mass near the kidney (usually only affects one kidney).
Spleen enlargement (splenomegaly) can sometimes be felt in the left-upper quadrant.
Stomach cancer can cause a mass in the left-upper abdomen in the stomach area (epigastric) if the cancer is large.
Uterine leiomyoma (fibroids) can cause a round, lumpy mass above the pelvis in the lower abdomen (sometimes can be felt if the fibroids are large).
Volvulus can cause a mass anywhere in the abdomen.
Ureteropelvic junction obstruction can cause a mass in the lower abdomen.