I was diagnosed with mono 4 days ago. and my spleen is enlarged. will it go down on its own? is garlic good for an enlarged spleen?

Yes: An enlarged spleen is seen in 50 to 60 percent of patients with infectious mononucleosis and usually begins to recede by the third week of the illness. I don't believe taking garlic will alter the course, symptoms, or signs of infectious mono.

Possibly beneficial: Elderberry reportedly has antiviral activity & thus may be beneficial against ebv that causes mono, & nadh (nicotinamide adenine dinucleotide hydrate) helps the mitochondria create atp, one of the body's energy molecules; so it may restore some of the energy that people with mono seem to have lost. As the viral illness resolves, the spleen will return to its normal size.