Since last september, after spending the day lifting heavy boxes and moving them around, I have had an odd feeling in my stomach, off and on. It doesn't exist when sitting, lying down, etc. When I stand and bend over a little, my stomach muscles, just below my naval feel like I just did 100 situps. Not crampy or painful, but the tight feeling after exercising.

If I go outside, to the store, etc. It doesn't seem to bother. It disappeared for about a month, but is back again.

If this was cancer, would it be felt no matter if I was standing, sitting, etc.?