I have been experiencing very severe cramps, nausea, mood swings ...

i can only tell you about my experience, i suffered with mine for four months, i had the same symptoms as yourself, sever cramps, nausea, mood swings, was suicidal the lot, to me its not worth it, it cured my heavy bleeding, but the side effects were worse than the cure. You have to do what is right for you... only you can decide how much pain you can take and how long you want to give it a go...

i hope you got on ok at the doctors, unfortunately most doctors dont recognise that these are genuine side effects and deny that Mirena is causing them....