I think you shouldn't be taking out Mirenas and trying to get pregnant without doctor approval, especially if it is dangerous for the mother. If it's a weight issue, it is also dangerous for the baby's future health, giving the baby a higher risk of diabetes.
But given that you are doing this anyway no matter what the doctor says or what I might think, at least don't compound the problem by developing a theory that your doctor is lying just like some other doctor did a year ago. That is simply talking like a crazy conspiracy theorist. A doctor who lies to a patient can be sued for malpractice. Finding two in a row who would do the same thing, lying about the same thing, is a ridiculous supposition.
If you want to check whether someone is pregnant, have them take an early-results home pregnancy test and keep taking them every few days until either she gets a positive or gets a period. It's not hard. At least you won't think a pregnancy test is lying the way you are developing a folie a deux that the doctor is lying.
Birth-control pills do not make a pregnancy fail.
Hi, she's been tested in a way by her doctor that really indicates she is not currently pregnant. Hormonal issues can cause pregnancy symptoms and delayed periods and this is not uncommon when coming off of birth control. I would look for her period to start and hopefully regulate and then it will be easier to try to conceive. On at 10 of her cycle, begin having sex every other day for the next 10 days is a good way to catch that egg. good luck