Yeah, no female flowers at first is normal (although it's not always the case). For the most part, you just need to wait. They should come. If you want fertilizer that might help, I recommend
monopotassium phosphate or
monoammonium phosphate. Phosphorus helps plants mature, helps with flowers, and even helps fruit ripen faster (so I've read and believe). Melons (C. melo only) like supplemental potassium a lot (watermelons don't seem to benefit nearly as much from it); so, monopotassium phosphate is probably the best choice of those two, if you're wanting to experiment with phosphorus. Potassium can help with fruit size/quality, plant strength, heat-tolerance, and other stuff.
I usually give my C. melo melons potassium (monopotassium phosphate, or
potassium sulfate with monoammonium phosphate) at transplant time.
Anyway, you don't need to add extra phosphorus, but IMO, the plants will probably like it, and probably flower and fruit more.
Watering the plants should help, too. I like to practically dry farm my melons (although I do water if I deem it particularly important), but they do grow more with more water, in my experience.
Extra sun helps, too. If the plants are partially shaded, they may take longer to get ripe fruit.
I wouldn't worry.
If you really want to give your C. melo melons a boost, I recommend supporting at least the first two or three feet of the plant with such as a cage (wider than a tomato cage). It seems to boost production in my garden, anyway.