I had sex on 15th march and periods on 17 th of march. but this month the periods has not came yet and i am not feeling an my pain? my age is 20 years. my partner used condoms during sex. so kindly tell what's the problems why it is not coming?

Do urine preg test: I would recommend purchasing a home urine pregnancy test first and testing. Home urine pregnancy tests are very accurate these days. If the home test is negative, I would continue to monitor to see if your period returns. Sometimes there can be a delay in the period due to stress and other factors. If the period remains gone, and your home test is negative, you should get lab work done by the Dr

Several reasons : If you have not had sex again since 15March (with a normal period after that) a pregnancy would be unlikely, but home pregnancy tests are quite accurate so reasonable to do one of those since period now late. If negative, late period could be due to stress (COVID19, etc), thyroid problems, or a few other causes which Dr could evaluate.