I'm on my second Mirena, and personally I love it. I see you've posted a few questions recently about it so it sounds like you're having some wacky symptoms. I know (and some people posted below) a few people that this form of BC just didn't work for, it made them crazy, etc. But I know others, myself included, who love it and have had zero problems. If you feel like you're in the first category, get rid of it. Personally, I might wait it out a few more months to see if you get used to it. I will say that the first 1-3 months are a bit whacky with irregular bleeding, etc.
Mirena makes the uterus an inhospitable environment for a fertilized egg, that's how it works. You might stop ovulating, you might not, but even if you do ovulate and that egg does get fertilized you have a very low chance of it actually implanting and resulting in pregnancy. No BC is 100%.
You can see your doctor and he/she can check to see that the Mirena string is still visible. If it's still visible that means it's still in place and your chance of pregnancy is slim to none. It's my understanding that most pregnancies that occur while on Mirena happen when it gets moved/dislodged, which sounds super yucky I know, but I don't think it's common.
I seriously doubt your are pregnant but if you feel crazed and hormonal all the time then maybe this isn't the option for you.