How can I get rid of stubborn pre-period pimples?

Consider derm MD. There are many potential treatments including the use of specific oral contraceptives. Other medication regimens may be instituted including skin care but clearly this is more hormonally related and would respond appropriately to hormone intervention with acceptance of the potential side effects.
Exfoliate. This is caused by hormone surges. Birth control pills can help but exfoliation one week before period helps, topical anti-biotic pads are great and benzyl peroxide works too.

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I'm having black heads on my face which are turning into pimples after some period! How to get rid of these black heads??

See below. Try washing your face with soap and water frequently during the day. Give it 3-4 weeks to see an effect. If that does not help, consult this site for home remedies. http://www.home-remedies-for-you.com/remedy/Pimples.html. Read more...