thanks for using health care magic.
You did a correct thing in first of all taking a pregnancy
which turned out negative.
Though 39 days is longer than the 32 days maximum of your cycle
and the conventionally accepted maximum of 35 days for a normal cycle,
single variation is hardly a call for concern unless when it becomes
repetitive. This could be due to a slight modification of the hormonal
equilibrium which is not permanent and will regularize subsequently.
However, repetitive prolonged periods
would have an underlying reason;
ovarian cystic disease, anovulatory disease etc.
What you should do is to re do the pregnancy test, if it comes back negative,then pregnancy would be definitely ruled out then use a temperature chart to monitor your daily morning temperature as you get up from bed to identify the probable date of ovulation (marked by increase temperature).
Best regards and hope this helps you.