Had unprotected sex in the middle of october and i have had regular periods every month since . can i be pregnant? its now january

No: you don't have regular periods when you are pregnant. If you need to convince yourself do a home pregnancy test.

Possible, not likely: It is possible to have regular periods and be pregnant, but not likely. If you still fear you may be pregnant, do a test. It should be positive by now. Need to use protection if you don't want to be pregnant.

Highly unlikely : It is highly unlikely that you conceived at the time of unprotected intercourse in October and have been having regular periods since. That does not mean you could not have conceived more recently if you have continued having unprotected intercourse and be pregnant now. When in doubt check a pregnancy test. Hope this helps.