I had sex, sept 8 &10th. i'm on the pill, normal 28 day cycle. lst period aug 16-bleeding yesterday. dnt know if it's implantation bleeding or period?

Menses: Assuming that you're taking your oral contraceptive (birth control) pill as directed at approximately the same time daily, chances of getting pregnant are pretty slim, tho never zero. However, spotting btwn periods isn't uncommon in young women. So most likely, you're starting your period (which should be during final week of pills). Regular use of condoms further reduces pregnancy & STI/STD risk.

Test test test: Very common question and the only way anyone can tell you for sure which it is involves checking at least a urine pregnancy test. However, some women will also have breakthrough bleeding on their pill and if that is persistent then you may need a different birth control pill. IF bleeding was after sex, that can be a sign of cervical infection as well.

Missed cycle?: If you miss an entire cycle, do a home pregnancy test- the only way to determine short of a formal blood test. This may be breakthrough bleedings due to normal hormonal mid cycle surge or fluctuation.Keep a menstrual diary and see if you miss a complete cycle.

OCP's: Did you miss any pills? Assuming that you are taking your pills correctly and your last episode of bleeding was the 16th of August, then your bleeding should begin again around the 13th of September. You are taking the pills for contraception. If you take the pills correctly then pregnancy should not have to be an issue. The wise choice here would be for you to use condoms also to protect you.

Your period.: Implantation bleeding is a very small amount of bleeding like one spot or 2 spots and it is rare. So the bleeding you are having is most probably is your period. I hope this helps.