I was written up for absences after using fmla and later fired for an unrelated reason that was false. is this retaliation?

It is unlawful retaliation if you were terminated due to your use of FMLA.  There is no way to tell without much, much more information whether there is sufficient evidence to support an FMLA retaliation claim.  I recommend that you consult with an experienced employment attorney as soon as possible if you believe the termination was due to your use of FMLA.