Don't know where to start

I have three kids and my fiancé has three kids I have been trying for over a year for a fourth child I love kids and this will be my last child do to the fact that I only want four I have had the mirena tooken out a year ago and I can't seem to get pregnant I don't know if it's me or my fiancé that can't conceive no more it's just strange to me or could it be that something went wrong with the mirena