Plz help my four month old cant lift head or roll over?

hi my lo is 4 months and as of yet she cant lift her head when on her tummy and isnt as of yet grabbing for toys.although she can keep the hold of things if givin to her but onli for short time. she can lift her head a wee bit on her back and is tryin to pull herself up when on her back. she dosnt seem interested in toys like reaching for them and im gettin worried.also she was 4 weeks early could this be something to consider.altho she dosnt seem to be hittin the 3 month milestones either.she can keep her head up when sittin up (gettin held).