It seems that my abdominal part is swallen.i didn't put on weight, eatting with no change.what is the problem?

Hard to tell but,: With no weight gain and with no change in eating habbits and with no pain, an abdominal swelling may be consistent with gas or constipation. The former (gas) may be associated with some form of indigestion. If not better, a visit to your doctor will be necessary to get medical history, examin and poss do an ultrasound. However, otc products for managing constipation may be the thing to do now.

Need more info: How much do you weigh? With age your fat may be redistributing and gathering on your belly more than in other places. If you are even slightly overweight try to lose weight through diet and exercise, easier said than done.