What causes 2 days periods for two months in a row? had unprotected sex before this started?

Many possibilities: The first thing to do here would be to take a pregnancy test and seek urgent attention if positive to exclude early pregnancy problems/issues. Other possibilities include medical conditions such as a thyroid problem (among others) that might be causing a change in the pattern of your periods (infection is possible too although less likely). See dr to arrange examination and tests. All the best.

Hormonal imbalance: Menstrual irregularities are not uncommon and anovulatory cycle is a common cause. If you miss more than two periods it would be time to see your doctor. If you do not wish to be pregnant, use contraception all the time. You may consider implanted contraceptive or an IUD. Consult this site for more information on this topic. http://www.nichd.nih.gov/health/topics/menstruation/conditioninfo/Pages/causes.aspx Practice safe sex, if you have sex.