I've always had a hard time paying attention in school, and it's getting worse. I cannot focus at all. What could I do to help? I've tried focus formula's from nutrition stores.

Understand basics. You are most likely to perform at your best (focus) when: you have adequate sleep, are free from hunger,are in a comfortable environment (stress free) and are free from illness. If trying to get by on <8 hrs of sleep and skimp on nutrition, stop. Get your doc to do a checkup. If your sleep/diet and health are fine, you can discuss any other suggestions the doc will have.
find the etiology. Poor focus could be coming from all sorts of things, from depression to add to malnutrition or stress etc. Consult a physician to rule out these etiologies then treat accordingly.
Paying attention. If this applies across-the-board to subjects, rather than just the subjects that you find boring or poorly-taught, you may have one of the attention-deficit disorders in your brain wiring and may be a candidate for medication. If you can stay focused on working problems, or on ordinary play, that's great. "Focus formula" concoctions from health-food stores are health frauds. Best wishes.
You . You should call your doctor and discuss your symptoms. Many people suffer from attention deficit disorder, but sometimes other problems such as depression and anxiety can also masquerade as an inability to concentrate. This is why an appointment with your doctor is so important - proper diagnosis is key to fixing the problem. Good luck!