Hello, I would be happy to help you with your question.
First of all, the symptoms of spotting within the first few months of the IUD being inserted is completely normal. Also, putting you on a low dose
progesterone pill was also very appropriate and hopefully improved your spotting.
In terms of chances of
pregnancy, it is extremely unusual in the setting of an IUD in the proper location. In fact, the chance of pregnancy with a
Mirena IUD is about the same as the chance of pregnancy after a tubal ligation!!
With regard to the addition of a low dose progesterone, this has the effect of stabilizing bleeding from the lining, but it also serves to thicken the cervical mucus, FURTHER decreasing the chance that sperm can get to an egg.
So in answer to your question, I think that the chance of pregnancy is EXTREMELY LOW and was made even less likely by the progesterone that you are on.
I hope this helps, good luck!!