A Depo-Provera shot usually provide pregnancy prevention for 3 months from the time it's given.
Afterwards, it may take several months for the periods to get back to a normal cycle.
If it was 3 months past when the Depo-Provera was given, there is a risk of pregnancy.
As you have given Depo shot in May then it would give you protection for June,July,August.
And if you have history of unprotected sex in September then there was a risk of pregnancy.
However if you are breastfeeding then possibly it is Lactational amenorrhea which causing you missed period.
You should undergo a home pregnancy test and using first morning urine will be most accurate earlier.
And consult your Obs/Gyn doctor as well.
Hope this helps.
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