Are my goldfish fighting or mating?

Well I have 4 goldfish in a huge tank together and there all probably about 2 and a half inches, except for the one thats probably about 3 and a half or 4. All of them are orange except one thats white. They keep chasing each other around the tank and rubbing up against each other on the sides and corners. At first it was only 3 of them doing it, but now all of them are doing it to each other. There mainly chaseing the white one, but sometimes the orange ones do it to other orange ones. They keep chaseing the white one and they try to get under him and suck, like when they eat... Haha its weird.. My mom had the water changed recently but I dont think thats the problem.. What do you think?