Period always on time , unprotected sex period 5 days late then light bleeding turned into spotting lasted 4 days. neg test at 9/12 dpo . pregnant?

Pregnant?: There are too many abbreviations and no punctuation so the timeline is hard to sort out. If you are a young healthy sexually active female, you could be pregnant. Not sure relatively speaking when preg test negative but repeat it two weeks after the first and you should have a more definitive answer.

Certainly possible.: I don't know what you mean by "9/12 DPO" but can offer some generalities. Since your periods are regular, it's likely that you ovulate regularly. There is about a 4-5 day window each month during which intercourse can result in conception. It's not uncommon to have mild bleeding/spotting when the embryo implants in the uterus. Do a 2nd pregnancy test if your period is another week late.