bella,
this time of year is infamous for robbing behavior........how to tell? bees flying frantically in a frenzy.... or lots of bees in the air in front of or on the hive being robbed; and an elevated 'roar' or 'hum' at the hive. robber bees tend to fly lower to the hive entrance/s (and many bees) and are intent on one thing.....finding any opening to the hive they want to rob. not like orientation flights where bees exit and fly up and down and face the hive to orient themselves. robber bees just want to get in. also, bees fighting at the entrance...tumbling, rolling around. bits of comb on the bottom board or on the landing board in front of the hive. if you look inside the hive, comb will be raggedly chewed and emptied of any honey that robbers can carry off. sometimes the queen can be killed in the process.
not sure what you have going on but reduce the hive entrance to the smallest opening. i use robbing screens, a screen placed on the front of the hive to help the bees defend their hive and reduce robbing. i also place these on every hive when robbing starts or before i think i might have a robbing situation.
hope this helps.....give us a few more details to help you out! iddee has plans here on the forum to build your own robbing screens, pretty simple, and effective!