I'm getting bruises in the palms of my hands and fingers with no reason any ideas why?

[Roxy]

I teach a fitness class once a week, and i realized the bruises showed up after I had my class not every week but when it did, it was the same day after the class, the bruises come on different sizes the little ones disappeared next day or same day and the big one takes two days to be gone, my blood tests were normal, doctors said not too worry about it..
Well forgot to say the class i teach is Zumba (dance fitness) so i really don't do any presure in m y hands say

 

[Blackwing]

You probably hit your hand or applied too much pressure on it (probably from your exercise moves or something) and didn't notice it.