The most fertile time to try for a baby is at mid-cycle. Pregnancy
occurs when there is sex around the time of
ovulation, that is around 14th day in a 28 day regular cycle. So if you try at this time, then there will be increased chances of a pregnancy. If no results even then, then you should consult a gynaecologist for investigations. Some underlying cause may be preventing a pregnancy.
Take care & good luck.