Hello
Thanks for posting your query at DoctorSpring.com
It is less likely to be implantation bleeding.
This is because a condom was used, and your last period was on 9th of August, so ovulation around the 26th is less likely.
I think that following pill stoppage, some amount of irregular cycles DO persist.
Considering your last sexual act on 26th August, it is too early to take the test right now.
Wait for a week more and take a test.
Give yourself one cycle to wait and see what happens, assuming that it is because of the pill.
If the same happens next month, have a gynecological check up.
An internal exam, a pelvic scan and basic hormonal levels ( FSH, LH, TSH, Prolactin ) should be checked to arrive at the cause of the irregularity.
Take care.
Feel free to discuss further.