A rash/pimples under the skin on the forehead can be caused from perspiration (clogged pores.) It's important to cleanse your face a couple of times a day with an oil-free cleanser. There are some very good ones at your local drug store. Often athletes such as football players or hockey players can get this problem.
Also, for women, (even men) any hair that is hanging on the forehead (and if you have oily hair) can clog pours. Just cleanse the face twice daily with oil-free cleanser, and apply wash with warm water, then cool (to close the pores.) Pat dry. You can ask your pharmacist for a cream from stopping your skin from flaking. There are so many good products out on the market and some are not expensive at all.
If this does not work (I am almost sure it will) then you may have a hormone problem, but only if you have these bumps all over your face. Forehead bumps are usually clogged pores.