Is There A Possibility Of Getting Pregnant?

Patient: Hi Im 19 and My period was on the 10th and ended the 12th of October, I had unprotected sex on the 16th of Oct, around 1 to 2am and my boyfriend ejaculated inside me. I have a 23 day cycle sometimes a 26 day depends on the moon. Is there a possibility of pregnancy? If yes how do I know how to calculate how many weeks I am?