pregnant with mirena?

I am 7 months postpartum with mirena, which I got at 2 months postpartum. My experience with mirena is not like most. I bled for a month and a half straight after getting it. I've had 2-3 week long periods every month ever since. Problem is I am a week late which is super abnormal. Typically I spot the week leading up to it, have a heavy flow the week of, and spot the week afterwards. My breasts are tender & swollen, my nose is stuffy, and I'm peeing frequently. I've taken 2 tests, both negative. Any ideas on what's going on?