Can I clarify:
Your last period started 42 days ago. Your bleeding last for 3 days plus irregular spotting. You also have had bleeding after intercourse.
How did you test for pregnancy?
Do you take any medication?
Assuming pregnancy has definitely been ruled out by the two negative tests, there are a number of other reasons for late or erratic period.
These include hormone imbalance, Polycystic Ovary Syndrome itself, thyroid problems, stress, being underweight, or being excessively overweight, losing weight very quickly or exercising excessively.
So you can see that there is a number of possible causes, but the link with your PCOS and the medication is the most likely cause. You should also have a smear test to rule out a problem with the cervix if your pap smears are not up to date.
Depending on whether you are looking to achieve a pregnancy at the moment then your doctor will plan your medication depending on this.