If you have more than one hive, or there are other hives near by, you could be getting robbed out. Some other symptoms would be wax crumbles on the bottom board etc. If you have very few bees, and there is very little stored honey, but lots of activity you are getting robbed. Also robbing bees just seem more hostile than bees coming and going into there own hive.
If you think you have enough bees to make a viable coloney screen them in tonight with some window screen, and staples. Move them to a friends house or a place a couple of miles away. Use a rope or a strap of some kind to keep the hive from coming appart. In the morning leave the screen on, but peel back a little bit to let the bees out like 1/2". With any luck if you are getting robbed out the field bees from the other hive will become field bees for your hive.
If things settle down and coloney starts to build up remove the screen but watch for hostile beehavior. Let the hive get strong like 8-10 frames, and move it back if you want. Do you have more than one hive? Or an established coloney some where so you can observe normal bee comings and goings?
I did the same thing this spring with two hives that were getting robbed due to my stupidity. I lost one which was week before the trouble started, and saved the other which is up to 6-8 frames from 50 bees and a confused queen. I was able to add a couple of frames of bees and brood from another hive though.