Is it wrongful termination if I was fired because I missed work for medical reasons?

The fact is that you can be terminated for an unexcused absence even it it was due to a medical condition. That is unless you had PTO or sick leave to cover your absence or were covered under FMLA (i.e. the Family Medical Leave Act). Otherwise, ansent some sort of protection under the terms of an employment contract or union agreement, you have no claim here. As an "at will" worker, you could have been fired for the reason that you cite, or for any reason or no reason at all. Further, since missing work constitutes "cause", you are not eligible for unemployment benefits. 

If you had and used paid time offf (PTO) which you had accrued for the absences, you could not be fired. You also could not be fired if your workplace was covered by the Family and Medical Leave Act (FMLA), which means that it had at least 50 employees within a 75-mile radius, you were eligible for FMLA (worked there at least a year and worked at least 1,250 hours in the past 12 months), and your illnesses and your child's are conditions that would let you use FMLA--and you did in fact use FMLA.
But other than using PTO or FMLA to cover medical-based absences, there is no right to miss work for medical reasons or to care for a family member. If you did miss work for absences not covered by PTO or FMLA, those were unauthorized absences and you could be terminated "for cause," which means no unemployment benefits. U.S. law simply does not give you an unlimited right to miss work for medical reasons, or require employers to retain employees who miss work.