do you have plaster walls or stucco interior walls, if so they're thicker than wallboard so the signal won't go through them as easily.

Also if your bathroom is in between the router and bedroom and you have tile on the walls, the signal won't go through as easily.

Look online for wifi extenders, they're suppose to help boost a wifi signal. You would plug it in between your bedroom and the router, if you have a hallway in between the two, that's normally a good place to plug it in. I don't think wifi extenders are brand name exclusive but there is a slight chance that your router will only work with certain ones, google it to find the right one for you.