I don't know if you have bangs but if you do that's probably why. If you don't, I'd ask a doctor or a dermatologist
Why do I get pimples on my forehead?
When you get pimples on your forehead, your hair can be one of the reasons (though you have mentioned that your hair does not touch your face). I also went through the same problem. The dermatologist said that it could be due to the unseen bacteria or germs or even dirt from our hair that causes pimples or mild eruptions on our skin, in this case, your forehead. So proper hair care is a must to keep your face clean from all kind of blemishes. Regular hair wash is a must and if you have dandruff problems, please treat that soon. Dandruff can also cause pimples on your forehead.
Have you tried any homemade face packs to treat your pimples? Cream from milk, turmeric, sandalwood powder and few drops of lemon juice is a pack that I used to treat my pimples. It does work but the effect is a little slow.
In my case, I tried a lot of homemade stuff but finally, the gel that dermatologist prescribed cured my pimples. Try consulting a dermatologist soon. :)
A lot of hair products are notorious for clogging pores, especially if you have bangs. The oils from your hair and scalp can clog pores too. The best thing I learned is to shampoo and condition BEFORE you wash your face and body because a lot of conditioners can cause pimples.