Those marks could be traumatic ones and nothing to be worried about.
But, if you get small spots all over your body at once then you should be worried. Those are called as petechiae and occur due to platelet deficiency. But, the spots you described are more so of traumatic nature. I suggest you do the folkowing,
1. Maintain a diary as to where the spots appear, the date it appears and disappears. Also note if you had a trauma or the activities before you got each of spot.
2. If you can also mention the size of spot each time it appears.
3. If the spot on your breast develops into a lump and there is pain, I suggest you visit a surgeon.
4. I suggest you maintain this diary for 1 week, if you finfmd there is no trauma being the cause. You might need to do few blood tests including the bleeding time, platelet time etc