Lost 13 pounds in weight in about 2 to 3 months, without exercise or dieting. should i be concerned? which body part should i be concerned about?

See md asap: Unexplained, unwanted weight loss could be due to overactive thyroid, occult infection, tumor; depression always in differential diagnosis. See md.

Depends.: without an exam, I can only give general information. Other signs of illness (fever, change in bowel/bladder), or organ dysfunction (can't breath, can't pee). A good context for a check up.