What causes freckles to suddenly become darker?

It's not even summer, but I'm frustrated by the increased number of tiny freckles on my face when I look in the mirror. I thought I was applying sunscreen diligently, but it's frustrating not knowing the exact cause of my freckles. I know there's a genetic component, but I'm wondering what habits I should adopt to address the sudden worsening of my freckles.
I'm curious whether my freckles are simply caused by sunlight or if there are other environmental factors, so I'm asking on the bulletin board before visiting the hospital. If you consult with Dr. Maypure, she'll explain everything from the cause of freckles to treatment options. I look forward to hearing from anyone who, like me, has been troubled by sudden skin changes.