A lot many factors play a role in conception and some of them are unknown to man.
with medicines like fertyl
is a hit and trial method.every female menstruates every month and ovulates every month.during ovulation,an egg is released from the ovary and it travells through the fallopian tube
Fertyl stimulates the ovary to produce more eggs so that more chances of pregnancy
Usually this is paralleled by ovulation study where the doctor analysis the size of the maturing follicles(egg) every alternate day(usually) and advises you to have intercourse on the day the follicle is ruptured.
Otherwise,the mid cycle period is favourable for pregnancy( in a female with normal menses).
If this doesn't work,this should be followed by a HSG
(hysterosalpingogram) to see if the fallopian tubes are patent and allow the passage of the egg.if required ,this should be followed by a diagnostic laproscopy.