Androgens (hormones) in our bodies stimulate the sebaceous (oil) glands. If your body produces too much androgen, or you are particularly sensitive to the effects of these hormones your skin will become oily. Bacteria on the skin feeds of this oil (sebum) and inflammed acne spots result.
Acne effects virtually all young people and 40% of adults between 25 and 40. It is not usually caused by diet or stress, some people are just more sensitive to the effects of androgens than others.
See your doctor for a course of oral antibiotics such as Doxycycline or Lymecycline. These kill the acne-causing bacteria on the skin. A topical retinoid such as Differin or Retin-a will also be helpful.
Don't use a moisturiser for dry skin whilst you are prone to acne. Use an oil-free SPF which does not block pores. Moderate exposure to UV light can improve acne.
The condition you're describing is probably not typical acne. usage of the sun block is probably blocking up your pores on the skin and that is not taking into consideration the make-up you use. In other words it could be a benign condition called "Folliculitis." Stop using the sun block, wash your face with an unscented facial soap and don't irritate it anymore. Irritation will cause eruptions and try to stay away from usual amount of make-up.
When your skin clears up, use a Facial Clarifier to unclog the pores. Eat more fresh fruit than you usually do because it has Beta Hydroxy Acids that will help by making you shed more skin. You want to exfoliate or shed skin cells more than usual because it will naturally open up the pores. That is what we want to do.
Avoid the sun during peak times of the day, which is from 10 am to 2 pm, wear a wide-brimmed hat and don't worry too much. If you have itches, don't scratch and always keep the skin as clean as possible. Don't touch your face because dirt on our hands tends to block up more pores. A facial clarifier is without prescription, so ask local pharmacist for one that is weaker than the others. The goal is to open up the skin pores without further irritating the skin.
If it causes alot of itchiness, take Daytime Antihistimaines. Antihistamines tend to make you drowsy, so Daytime formulas are mixed with something to keep you up and alert.
Incidentally, when I was in medical school, I had a friend who took antihistamines that weren't Daytime formula, so we saw him in the morning on an office couch trying to sleep, we saw him in class fast asleep and finally went home like he couldn't make it on his own.
Remember, use Daytime formulas, OK?