Guinea pig getting bullied?

my piggies were getting along fine they are both female one is 4 month old the other three and a half month old. the bigger one has strted sitting on the little one and trying to hump it and the little one kind of grumbles at it to get off and the big one teeth chatters and the little one runs of in the house. also it chases it away from food. they dont fight, they sort it out between them, but i am concerened the little one is unhappy and not getting enough food. will they settle down? x