If they look hungry, feed them. Do you know how many weeks total 'till they're ready to harvest? If so feed them up to a week or more before you harvest. At four weeks most girls are starting to put on the weight, (kinda like a wife at four years!), so they need food to be able to be all you want them to be.
Some don't look like they're fattening up until the last couple of weeks and some are fat by four weeks then grow slowly to harvest time. You don't mention what type of grow you're doing but any grow at four weeks flowering needs some feeding or be in super soil.