Do I have dandruff or a different condition?

Ever since... maybe May?.. I've had issues with sand-like particles on my scalp. I've had dandruff before but I don't remember the particles feeling harder like sand. Also, my head tends to itch every so often. I've tried Head and Shoulders and Scalp Benefits by Aveda thinking one of these would solve my problem.. no luck. My dad said it's only because I'm a teenager (i'm fifteen). I feel like it's more than just my age. Also, I'm having to wash my hair every day because the amount of grease after a day makes my hair look like I haven't bathed in weeks. Any clue?