Why am I just now getting a ton of acne?

Okay, so I'm 15, almost 16. My whole life, I've always had really nice skin. I rarely would ever get pimples. I've notieced that past month or two, I've been getting a lot more acne. I've tried a ton of products, mainly all drug store, except I've tried clinique 3 step. I have pretty dry skin, and I keep getting pimples on my forehead! My cheek area is pefect, no pimples at all, but on my foreheard i've got like 6 or 7 pimples. When I cover it up, it looks pretty good, but I want to get rid of them!
Any tips?
I switched the makeup I was using too, and nothings changed. My mom won't take me to a dermatologist,but she said she won't mind buying me something like Proactiv.
So I need a good product for my forehead, to clear pimples/redness for normal to dry skin.
I take good care of my skin. I wash off my makeup every night, and i always cleanse, tone, and moisturize.
I just don't understand why now I'm getting acne. Does that mean anything?