No, you are probably not eligible for the new Post 9/11 GI Bill, although I recommend you make an appointment to speak with a VA benefits counselor before you separate to make sure.
Your medical retirement will follow an honorable discharge, which is one of the requirements for the GI Bill. You have served about 4 years, and I will assume that you mean 4 years of active duty service. The new GI Bill only requires 90 consecutive days of service that fall after the date of September 11, 2001, and the benefits reach 100% tuition when you hit 36 months of qualifying active duty.
However, the service that you use to qualify for the new GI Bill cannot also be used to qualify for another education benefit. In order for your active duty service to count toward the new GI Bill, you would first have to complete the service obligation your accrued for your military academy education. The same would go for an ROTC officer who didn’t complete his obligation.