Replying to Internet gradually not working mac

Over the past week and a half I've noticed my internet is gradually deteriorating. I;ve had my macbook pro since 2009 and am wondering if something is wrong? Webpages are loading slower, if at all, and I constantly have to close/re-open browsers. I finally upgraded from leopard to mountain lion over a month ago, and it worked fine the first few weeks. Now I am getting annoyed and concerned. Anyone else have this happen and know any solutions?