Hi there,

Is there any chance you are pregnant? If Af is late and you are having some pain then it's possible.
If you think theres no chance then I guess you could be ovulating late but are there other signs ie. fertile mc or ovulation pain?? If you usually ovulate around day 17, did you have any of those signs happening around then?
If you did O on day 17 then perhaps the pain you have now is a) pre menstrual funniness, b) implantation pain (it's about 10 dpo?) or c) early pregnancy symptoms.

You could do a HPT but it could be too early to get a positive.
Hope that helps...