Right after ovulation is when you'll probably feel the biggest changes in your sleep habits, Dr. Hernandez-Rey says. In addition to your rising progesterone level, "you'll have drops in melatonin and cortisol levels," he explains, "and that dysregulation is one of the reasons you might have insomnia."Both melatonin and cortisol play huge roles in your sleep-wake cycle. Cortisol's nickname of the "stress hormone" makes it sound like a bad thing, but it's actually really important for keeping you awake. (What makes it bad is when you have too much cortisol.) Drinking coffee the next day when you're tired can actually then make this effect worse because it suppresses your body's response to cortisol, meaning you're working against your natural alertness and might not actually feel that much more energized. So be careful with caffeine (a good idea anyway if you're dealing with insomnia), or at least do your best to time it right On the other hand, melatonin is a hormone known for its sleep-inducing properties . So Dr. Hernandez-Rey suggests that a melatonin supplement during these days might be extra effective if you're having trouble getting to sleep.