8o8sandra,
I'm not a doctor, so I can't give you a definitive answer to this question.
However, since both the shot and Migranal administer DHE, it may be best to stick with one or the other. You can suffer from symptoms after using too much of an ergotamine (which both meds are). You should definitely stick to the directions that you were given by your doctor (that are on the box).
Take a look at this article that gives you in depth info on using Migranal. Be careful to watch out for the overuse symptoms listed here.