I have reached a plateau?

i recently lost 20 pounds through proper dieting and exercise. I lost this weight at about 1 pound a week. I have noticed that in the last 4 weeks or so I have not lost anything. I have been gaining 1 or 2 pds and then lose it again but nothing more. What do I need to do?I run a lot and have increase my intensity as well as doing pushups but still. Please help cause I am beginning to get frustated to a point where I think I am going to backslide.