Sounds like your router is running in G mode, do you have older equipment that is connected wirelessly to your N router (assuming you have an N router otherwise that's your problem right there.)
I also have to assume you mean 50Mb/s not 50MB/s because the latter is 8x as fast.
Oh and one last thing very few sites will be able to give you a 50Mb/s connection so it could just be the site.