This is a tough situation and you really do not have a lot of options.
First of all, the laws currently in place in this country will not permit any current or former service member to sue the U.S. Government for inures he or she has suffered while serving on active military duty. This is the "Feres Doctrine," and it is pretty much an iron clad bat to filing any sort of tort claim or civil lawsuit against the Army in the situation you describe. Follow this link to read more about the Feres Doctrine: http://en.wikipedia.org/wiki/Feres_v._United_States
Instead of suing the Army, you might consider talking to an attorney who handles Veterans Affairs Claims. Depending on your injuries, you may be able to have such an attorney file a VA claim and if you win on your claim, you could receive a disability. This translates into a monthly check from the Government paying your health care and living expenses.
Yet another avenue of attack may be to file a review or an appeal to the Army Board for Correction of Military Records. These so called BMR appeals may result in a finding that the Army handled your discharge unlawfully or was against Army policy. If that happened you may be entitled to a better discharge characterization or perhaps even reinstatement with back pay.Ask a similar question