My datetime isn't formatted correctly, what have I done wrong?
Use the days property from the timedelta object you get when you subtract the dates.
Meaning:
a) remove changeInDateStr
b) make changeInDate global
c) change the print line to:
print [..blah blah...] " This was " + changeInDate.days + [" days", " day"][changeInDays.days==1] + " ago!"