My 11 year old daughter had a problem she bruised very easy and had to see hemotologist and was dx with a condition called IPT it is really something you should go to a doctor for there are some lesser conditions like enemia and more scary conditions so you should get checked out
Anemia is certainly a likely possibility. There are various kinds of anemia, with iron-deficient anemia being likely in a person at your age. A visit with your PCP, including a complete blood count (CBC) and several related tests to check for iron levels (serum iron, ferritin, etc) and such should help sort out what is going on.
Enemia! drink a lot of water, and take iron pills! but first get tested for enemia!