It could be. Switching drugs, even though they have the same purpose can cause an irregular menstrual cycle or other side effects. I really would talk to the doctor, or a nurse where you get the prescription and let them know about this side effect and what you should do, if anything. If it is because of the switch, or the missed pill, it should take care of itself.
There are other medical reasons, some of which are listed and discussed in an article written by Merely Me, a writer and community leader, for this site, titled, Bleeding In Between Periods. What does it mean?
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