I had a 1day heavy period &3light spotting days,could that be a result of plan b pill?or cause i workout too much that put my period on hold?

Both: Both could be causes of your period being on hold, as you say. When women don't have a lot of fat on their bodies, they often lose their menstrual cycle. Exercise, per se, doesn't cause loss of cycle. Plan B can also interrupt normal cycle as well, so it's hard to say which of these 2 is playing a role right now in your body. Calculate your BMI, normal is 19-25. That's a good place to start.