I have a 3 month old grandson whom his mumis not allowing me to see, do I have any rights

Are you the mom's or the dads mother ? If this is your daughter why is she not letting you see the child.

And if you are the fathers dad, why is he not letting you see the child when he gets his visitation ?

Some states are starting to allow grandparents some rights, but most states still do not do anything for grandparents,

You will need to contact a local attorney and talk to them, if your state has been reconising it, you may be able to file a motion in court for visitation rights.