HI,
Lump in abdomen can be because of various reasons depending on its location and size. The upper abdominal swellings are commonly from the liver, spleen, gall bladder or stomach. The lower abdomen swellings are commonly from the uterus, urinary bladder, and colon etc. The diagnosis of the same can be made by doing an ultrasound of the abdomen. If the ultrasound is not able to pick it up, then a CT scan of the abdomen can be done to look for the cause.
Hope this helps. Take care and good luck.