Thanks for your query.
Primolut is progesterone
preparation which is given to induce withdrawal bleeding in case of absent periods.
It cannot be responsible for a positive pregnancy
If the urine pregnancy test is positive, it means that your wife is really pregnant.
As she had irregular cycles, I would advise you to confirm the diagnosis by visiting a gynecologist, and having a blood B HCG
test, or a pelvic transvaginal ultrasound
Also, have reliable birth control methods if the menstrual cycles are irregular.