How to deal with bad past karma that makes my current life miserable? Before I practice Buddhism,I've made mistakes and hurt other. Sometimes I thought what happen to me now is the effect of what I did.
I try to  keep doing positive things but sometimes I could not stand this hard situation. Could anyone tell me please how to solve this situation in Buddhism way?
An understanding of what causes have contributed to the way we are right now is out of the realm of ordinary people; practically speaking, you are more likely to project a false impression of why you are the way you are that is wholly disproportionate in terms of cause and actual effect.

Much of what we are today has already been predetermined from the moment of our conception, including the nature of our body and our brain, our social status and community, and even our life choices and experiences to a certain extent.

That being said, karma performed in this life will certainly have an affect on our minds and influence our choices as well as our mental and physical well-being. Much of this is also out of our control, at least in terms of direct intervention.

What we can do is two things:


We can, as the Buddha taught Angulimala, "bear with" the unpleasant experiences. This has the effect of both neutralizing the mental suffering that comes from unpleasant experiences as well as nullifying any further bad karma we might create in reaction to the experience (thus potentially ending the cycle that caused the experience in the first place).
We can perform wholesome deeds like giving charity or help to others, abstaining from unethical deeds and speech, and practising meditation to calm and clarify our minds. This has the effect of acting as a buffer to our unwholesome deeds, in effect (potentially) counteracting them. As the Buddha taught to Angulimala:



  He, who by good deeds covers the evil he has done, 
  illuminates this world like the moon freed
  from clouds.
  
  -- Dhp. 173 (Buddharakkhita,trans)