Will thrush go away on its own? I have SLE (no organ damage). Bland and very bitter taste, and it smells. Tongue is slighly yellow otherwise normal

Not sure it is. I doubt what you have is thrust and the coloration of the tongue offers no help in making a diagnosis. I suspect that the bitter taste and odor may be from bile reflux instead. Contact your doctor.
And yes, thrush may go away on its own -quicker if treated.