You wouldn't be pregnant from your unprotected sex in September, but if you had sex in December or late November it's possible.
I'd recommend a pregnancy test - it's the only sure way to tell. But after all this time - you're probably not pregnant. I'd certainly doubt it, and since it's been three months, you would almost certainly know by now, because the first trimester is when you can feel the sickest. So please take a pregnancy test, but I highly doubt it.