Hi. I’m not certain, but I think it is probably yellow or white sweetclover (Melilotus officinalis or M. alba). If you let it stick around long enough to flower, it will be easy to confirm (or refute) that identification. If it is sweetclover, it is not a native plant, but rather an introduced one. Whether or not it is a weed somewhat depends on your perspective. It is considered a noxious weed in some areas but a useful forage plant in others. This publication from the USDA provides a lot of good information about the two species (which may be one in the same).