Was planning to get pregnant on dec but it did not happen, my periods came 5th and I had sex on 15th, 16th&17 but yesterday I got my periods...Please advic?

Try again. It is not unusual for a single cycle of intercourse to fail at conception. Sex occurred days 11, 12, and 13 of your cycle. You may not have ovulated yet. Try having sex that entire week.
Keep at it . Life does not always go exactly as we planned. We advise couples who are wanting to be pregnant to have intercourse for about one year before coming for fertility testing. You have been trying for one month. Keep at it but relax and dont think about trying to get pregnant so much. Anxiety does not help. Take a prenatal vitamin daily.