it is possible, and i would check the levels again in a week. me and my husband were using two forms of birth control as well when i got pregnant with our oldest. neither was an iud, but still. and we used them correctly. i know with our last pregnancy we found out really early. it was around three weeks. hormone levels also differ, and if you are it just may be too early to tell. it is also possible that you are not and that you are just having side effects due to the mirena. my cousin has had hers for less than a year and she feels like she is pregnant as well. but shes not. so my suggestion would be to check again in about a week, and if you arent to call the dr to discuss your symptoms. if you are, call immeditealy and discuss your options.