Lose of bandwidth when surfing the net

Hopefully I am in the right place here. The problem I have has occurred for a while 2months at the most. I have Comcast as a internet service provider and I use sprints broadband wireless card when I am out and about. Whenever I surf the net it seems I lose my connection. If I am downloading something at an avg 125kb. I leave that to surf and it drops to 0kbs. I can’t figure it out I checked all my settings and I still can’t figure it out but maybe I am missing something. Any help you guys can give me would be appreciated.