Your body, mainly your bones, wasn't creating near enough blood.

Thus, since you're his only child, he did everything in his power to keep you alive. He found that nanobots could potentially solve your problem, and put a lot of money into the research. It was a couple months before they were ready to inject you with the first batch, whose primary objective was to establish a link between your brain, the nanobots, and the major blood-making parts of your body. They did this, relatively effectively. You actually improved a bit, but nowhere near out of the grave. You were still confined to your bed.

So, they decided to inject you with some nanobots that would act as factories. They went, and from inside you, they created blood that was able to be controlled by the nanobots.

Same thing happened, so your father got nervous and ordered that some more be injected, only this time they'd be a mix of repair-men, immune-system replacements, and a variety of others. However, this killed you.

But, he refused to believe you were dead, because your body didn't decay, and whenever you would be cut, the cut would heal almost instantaneously.

He turned out to be right when you woke up as a better version of yourself.

You had somehow managed to gain a conscious hold over the nanobots, as demonstrated when you were angry, and punched a hole into a solid concrete wall with barely any injuries to yourself. You had somehow managed to harden your skin somehow, and you also managed to create things with your blood while it was outside your body.

This frightened the government, who took you into custody, and they thought you were an oppurtunity, because you were damn nigh invincible. They proved this after training you to control the nanobots better.

Then, you were betrayed by your favorite mentor, whom you then proceeded to kill. That's when they captured you.....and where our story will begin.