Anything that stresses your body so much can affect your monthly cycle. Add to that any meds you may be taking, and your cycle may well be erratic for a while.
Example: When I went on fluoxetine, there were no warnings about effects to my monthly cycle. I went from extremely heavy monthlies, to missing one month, followed by very light menses. I did some research, and found that menstrual cycles are generally not monitored for side effects when a drug is being tested, unless the drug is meant to affect the monthly cycle. There were so many women posting questions about the interaction of fluoxetine with their period, that I kinda took it as a given that lots of women have missed periods when going on to it.
Hope that helps, and use extra birth control just in case!