Generally, if you start on the first day of your period, they say you do not need to use backup because the chances of conceiving during your period are incredibly low.
However, if you're not sure that this is your period, there's no harm in starting it now (or whenever you like) and using backup protection for 7 days of active pills (after which point you are guaranteed to be protected, regardless of where you are in your cycle).
If this is right around your period time, it won't really affect much... it's certainly not bad for you. If it's a little early, you may experience a bit of breakthrough bleeding next week or around the time of your next period. But it's not bad per se.
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However, if you're not sure that this is your period, there's no harm in starting it now (or whenever you like) and using backup protection for 7 days of active pills (after which point you are guaranteed to be protected, regardless of where you are in your cycle).
If this is right around your period time, it won't really affect much... it's certainly not bad for you. If it's a little early, you may experience a bit of breakthrough bleeding next week or around the time of your next period. But it's not bad per se.