discharge

I was recently diagnosed with a disorder called cyclothymic disorder that causes severe mood swings. I am in the US Marine Corps and I was wondering, my doctor is putting in a recommendation to my commander to have be seperated from the Marine Corps. It was a Prior to Service illness that was never detected until know. What I was wondering was, can they deny a discharge even if recommended by a doctor? Would it be smart to get a civilian attorney or a JAG Attorney or to just wait it out? Is there any way under the UCMJ or other code or whatnot or contract that could speed the process up?

Thank you