I am sorry that your son is ill and that you are worried about him. If you could tell us some more information about your son, perhaps someone on this forum could answer your question. How old is your son, does he know what genotype of Hep C he has, has he had a liver biopsy to determine what stage of liver damage he may have? Has he had other vaccines to protect his liver (e.g. Hep A and Hep B)? Does he have another support system in place, since he doesn't want to worry you?
Since he is co-infected with both HIV and Hep C there are two viruses that his liver is trying to fight against right now. Hopefully he has a very good doctor, preferably a hepatologist.
I am so sorry, your son needs to see a hepatologist soon, 900 is high, perhaps he can work with your sons present doctor to come up with a treatment plan. There is treatment, has he had a biopsy?
I am a Mom as well, I can feel your pain, I am so very sorry. It is hard to be a Mom.
I am sure others will be here soon to help. As Advocate said, more information would help.
My best to you