When I was pregnant I used to bruise easily from things that shouldn't have caused bruising. I was very sick in my pregnancy and ended up with anemia and was told that this was causing me to bruise easily.
I think that the human body is an amazing thing and has it's way of telling us when something is not right. If you're bruising when you normally wouldn't, it's likely time to get checked out. If it's something like low iron, then it's worth getting this looked into so you can quickly remedy it.