Maryland has many crimes (including certain non-domestic assaults) that are "misdemeanors" but, unlike the traditional concept of misdemeanor crimes in most states, carry jail sentences in excess of one year (I am aware of some MD "misdemeanors" that carry up to 5 years in jail). If the misdemeanor carries more than 2 years in jail as the maximum possible sentence (regardless of the sentence actually imposed), it creates a federal firearm disability under 18 U.S.C. § 922(g)(1). See also 18 U.S.C. § 921(a)(20) (definitions).
You may have few options other than to contact a lawyer and determine whether your conviction triggered this federal disability. If so, you may have no option other than to seek a gubernatorial pardon,