Last month, period came on the 16th (a week late), this month suppose to come on 18th (or 19th), still hasn't. is it delayed?

Depends: Other than the late period last month, if your periods are regular, you are late. If you had unprotected sex since your last period you should do a pregnancy test. If it is negative repeat it in 4-5 days. Use first morning urine and follow the instructions for the test carefully. If you do not wish to be pregnant, use contraception all the time, every time. You may consider implanted contraceptive, or IUD. Practice safe sex.