Last month i had unprotected sex. he didn't came in me. the beginning of this month i started to have brown color from my vagina. missed period, why?

Hard to say: You may be pregnant.Any mucous from an erect penis has enough sperm to cause pregnancy (not just the main load). Unprotected sex is also a good way for you to get chlamydia or other STD's that may produce vague symptoms.

Several causes: for brown discharge. It may just be old blood mixed with normal vaginal mucous. (Old blood looks brown) It could also be the result of a common bacterial infection called bacterial vaginosis (BV). The best thing to do is have a pelvic exam so a sample of the discharge can be taken and a pregnancy test performed. BV is easily treated, but it needs to be confirmed before an Rx can be written.

Pregnancy : You should check to see if you are pregnant as sperm is released even without ejaculation.