Are you sure this is acne vulgaris? If it is then acne is due to hormonal imbalance - read the etiology of acne by Professor Hywel Williams, Nottingham University. However, I was quite impressed by a book called 'Acne no More' You might try reading this.

I think part of your answer may be in the first line of your post...."boil like spots". Its easy to assume that any bumps that come up on our face is acne. Often the assumption is correct. It sounds like this is not the typical run of the mill acne you have had in the past. You may actually have a skin infection. Its likely unrelated to the mirena - the hormones in mirena are localized not systemic like BC pills.

With that being said, I would try the following: try using a Neutrogena Clear Pore Cleanser/Mask (That is word for word what is on the label). Use it as a cleanser daily and then on the first day and maybe as often as every other day use it as a mask on the boil like spots only. Follow up with Neutrogena Rapid Clear Acne Eliminating Spot Gel (there are 2 versions of this - you do not want the orange gel in the translucent tube, you want the other one. Apply to gel to the spots only not your entire face twice a day (morning and night before bed). If it gets better you're on a good path. If it gets worse go see the doctor and when you call/go in for the appointment tell them just what you said above - boil like spots on my face, thought they were acne and have been treating them as acne for however long and no change/gotten worse.

One other thing...you just got the mirena, many women get it 6-9 weeks after giving birth - have you had a baby recently?

One more question I forgot to ask...what were you using for BC before mirena?

I think you must see a dermatologist.