How do I pick up the pace?

Considering your gender and age, that 3 mile time is pretty good. Increasing foot speed requires speed workouts (400m reps and 200m reps are the most common) the temp conditions you are running in is not too hot. Humidity is what kills a runner. When your sweat cant evaporate off your skin, your body cant cool down... and you know the rest. Increase speed by running more miles weekly and daily and your body will respond. running is just like building muscle. the more you tear it down, the stronger it will rebuild. Also, running is 90% mental and 10% physical. You have to grit you teeth sometimes and just get MEAN!