Please dont worry about asking a question like this - this is what the forums are for:)
I would suggest you get to the doctor right now, and ask to have a check - the mirena can move around and can become embedded into the side of the uterus and on occassions can perforate it and move to a completely different part of your body, both of which are obviously serious complications. Hopefully in your case, it has just moved further up the uterus, but the possibility of embedment or perforation is an important consideration and therefore you should not delay, just in case. Good luck, i hope you get on alright. Hugs x