Too early for periods to stop whilst using mirena IUS

Patient: Hi I had laparascopic surgery in late july for investigation and then treatment of endometriosis via diathermy where a small patch was found on my right ulterosaceral ligament. I was then put on Norethisterone for 3 months from the time of surgery to control heavy bleeding I was having during my periods before the surgery. I stopped taking this after two months after consulting my doctor as it was giving me awful side effects, but I never had a withdrawal bleed or any kind of period since, not even so much as a spot. I have the mirena and had it since late july when they fitted it during my surgery to help with the endometriosis, so I have not had a period since July. I didn’t think the mirena stopped periods so early on and have read information relating to periods stopping after about a year or so of having the mirena, and for them to be all over the place for the first 3-6 months. This is also what my gynae consultant told me. I have since had ultrasound scans as I am still experiencing endometriosis type pelvic pains, which revealed I also have adenomyosis. I have done 3 preganacy tests over the space of the past 2-3 weeks and all have been negative and so I am confused as to why I’ve not had any sort of bleed as yet and am not happy with them changing in such a drastic way?