Melon help please

I'm not sure what I'm doing wrong. I have watermelon and muskmelon planted in the greenhouse. They are almost the exact same size now, a month later, as they were when I planted them. Everything else in the greenhouse is doing great. What do I need to do to these things???

I have noticed my melons are behind everything else, too.  The squash are running away, the zucchini is  bigger than me and producing almost every day.  I might even have pumpkins in July!  The melons though, are not even a foot tall/long.  Mine are in the ground. I am in GA (US)