You need to have a diagnosis first as to why your spleen is enlarged. If it is due to mono then you need to wait until the virus subsides and the spleen will eventually return to normal size. Other causes may not be reversible.
Do not go to the ER for this. It is a chronic problem which needs to be addressed by your primary care physician who can then refer you to the proper specialist (surgeon, hematologist, GI doc etc.) If you don't have a PCP or insurance go find a primary care clinic.