Is the determining thought moment (vottopana) based entirely off of past karma? Is the way I choose to react to a situation based entirely off of past karma or is there something else that determines how I react to an external object?

I am confused between my understanding that ultimately there is no control and yet I can control my reactions to situations. Is there only a sense of control as long as an individual is not fully enlightened?
Vottapana is a Citta(thought moment) that has the function of determining or decision making. It is not a result of past Kamma. But it is not a self either. There's no 'I' in it. Why? Because it is also born of causes and impermanent like any other Citta. 


  there is no
  control and yet I can control my reactions to situations. Is there
  only a sense of control as long as an individual is not fully
  enlightened?


Whether one is enlightened or not, there's no sense of control if by 'control' you mean there's a 'self' or 'I' who does the decision making. But there's a sense of control in the sense of a citta performing the function of decision making.