you didn't mentioned exactly on which day of cycle you finished periods. If that was on 5th day of cycle, 5th of may will become 8th day of cycle.
normally 8th day to 20th day can be taken as the fertile period in 28 days cycle.
So, there is a possibility for pregnancy
. Remember it is only possibility.
Now i pill
will not work. You visit gynecologist once and undergo blood test
for pregnancy which will mostly rule out your doubt.