I have had the mirena iud for about 4 and a half yrs slowly my periods started to go away but recently in the last month my period has been on almost all month it starts with really bad lower back pain and really stomach cramps I have constant headaches and loss of appetite and nausea I really don't know if I am pregnant but I am scared to find out. Is this something that is likely?

If you still got the mirena iud , it is very unlikely that you would be pregnant.
Make an appointment with a specialist
And do not be afraid of finding out what is causing your latest problem.