Hi
I had a Mirena fitted in January (aged 59, 10 yrs post meno, 1yr on HRT and had bleeding, investigation showed slightly thickened womb lining so coil suggested). I bled for a couple of weeks and then it changed to what I described as dirty discharge. This carried on for several weeks, when I had my 6wk coil check the practice nurse seemed surprised I was still bleeding so asked me to go back after another 4wks. I was still having dirty discharge at that point so they checked with the gynae team at the hospital (where I'd had it fitted) and they said it could continue for 6 months or so! I have to admit that after 10yrs of no periods this did concern me and I questioned my decision to have the coil fitted! But, unlike you, I haven't had any pain at all.
The bleeding/discharge stopped after about 3mths but then I've had a couple of episodes of spotting since, I've started to keep a note of the dates to see if there is a pattern and to be able to tell my GP if I have to go back.
Maybe have a chat with your nurse when you have your 6week check, just to put your mind at rest.
Fingers crossed it stops for you soon
Sue