How can Buddhism help me to get rid of a suffering due to a disease? I came to know about Buddhism very late in my life. It is the time for me to relearn the fundamentals of life. But I struggle with everyday activity. I lack energy.  In fact I have a diabetes. My past Karma has been bad enough to get me a disease. 

My question is: How can Buddhism help me get rid of this disease? If I fix my Karma then will the suffering due to the disease will disappear ? If yes, how can I repent and to whom ?
I don't know your situation and haven't suffered anything like it, so any advice I have may mean nothing to you, but I will say these things:


Karma is the fruit of past action. Don't concern yourself with what's past, and focus on the actions you do in the present. The Buddha said that speculating about the workings of karma is a waste of time, because it is too complex, and (at best) only fully-enlightened beings can see the full chain of causes and effects that led us to where we are now, or where we will go in the future. Kindness and mindfulness in the present moment are our tools to create good karma. Taking care of your health is a part of kindness and mindfulness, because it is important to be kind and forgiving to yourself. If you condemn or harm yourself, you are condemning and harming a future being, so be kind to yourself.
Practicing the Dharma and ending suffering are long-term projects. You may not be able to cure the disease. But every moment of kindness and mindfulness erases a moment of future suffering. Repent to yourself first. If, as you do this, you're moved to repent or ask forgiveness from someone else, then do that, but don't put more pressure on yourself than the disease is already putting on you. Be kind to yourself.
Look at the body in a moment-by-moment way and watch the way energy and pain and sensation change in every single millisecond. Watch how feelings that you think last for minutes, days, or hours are actually fluctuating in every moment. Sometimes there are eruptions of pleasant in the middle of a painful feeling. Different parts of the body are feeling different sensations and energies at different moments. Karma doesn't just act on your life, but also on every single moment within your life- the truth is, you die and are reborn many times a second. Observe the bodily sensations as much as you can.
You will be low on energy, and so practice will be difficult. Forgive yourself for not being a great practitioner, and only do the best you are able to. Look into the mind and see if you can find that little part of your mind that's always fully alert, always watching itself, even when you feel that you're tired and your attention is weak. Use that part of your mind to watch the rest of your body and mind and know that none of it is "you" or "yours".
Disease and physical health are partly the result of karma, but also partly the result of the nature of being human in a world made of matter. To be born human is to be born with a body subject to disease and death. So don't blame yourself for what's part of your nature as a human being. To be born human also means being born to hear the Dharma and to be free to act kindly and mindfully in ways that will improve your future. The fact that your karma led to a human birth means that your past included more positive karmic influences than negative ones. So be kind to yourself.


May you be well.