What Causes Itchy Bumps All Over The Body?

Hi Doctor, I am 28 year Male, from few days I am having itchy bumps all over my body. First they look smaller in size and itches very much but if I itch that area then it spreads and covers a bigger area than it was earlier and swells. It happens all day but most at night after dinner and along with it I feel a heavy stomach pain at my upper abdominal area. Please help.