Not Sure if I should or not

I'm 26, married, but do not plan to have children any time soon. I was recently diagnosed with a seizure disorder and have been placed on an anti-convolsant to control the seizures, tegratol. The pills are working great for the seizures, but my hormones have been thrown out of wack. I get my period at different times of the month now, were I was as perfect as a clock before.
Along with the seizures I suffer from endometriosis. I have been on Levlen for 10 years and before the seizure drugs, I had no problems with the pill. My periods were light and almost pain free. Now I don't know when I will be in pain and my husband and I have had to use condoms, which we haven't done since we were first dating. I was told that the tegratol would affect the pill and to use added protection due to the possible risks of birth defects.
Now to the question. I have seen and heard a lot about Mirena and it benefits, and now finding this site, I've read about its negatives. I was wondering if any women with endometriosis are using this IUD? How does it affect your periods (pain, amt ect)? What are the possible side effects with seizure meds? The main reason I was looking into it was so that I would not be able to get pregnant, due to the possible side effects of my tergatol, so and IUD is a good thing, but my endo means that I can't have the traditional copper type. I want my body back to normal. HELP please. Give me the goods and the bads. Tweet