You should go with your instinct, especially if you have coworkers who share you concern. Although, my own older son could have fit most of the things you said at one time or another... (he had the bathroom problems occassionally even last year in 1st grade, always bumps and bruises,etc...though they are congruent with the "normal" description below, usually shins).
If it helps, I would think about what kind of bruises/injuries he has - many times you can discern whether they are typical child play bruises or in atypical locations and patterns:
"Use common sense in trying to figure out if a child is being abused. For example, normal, active children get some bruises and bumps from everyday playing. These bruises are mostly over bony areas such as knees, elbows, and shins. But, if you see a child with injuries on other parts of the body, such as the stomach, cheeks, ears, buttocks, mouth, or thighs, you should think twice. Black eyes, human bite marks, and round burns the size of a cigarette, don't come from everyday play."
More that may be helpful: