I have read that you can get pregnant from "pre ejaculation"?

I am 22 years old and still a virgin. The other day I went to see a friend at work and he got turned on but we couldn't do anything. I left and he wanted me to come back and hour later to see him for lunch so I did. I was supposed to start my period either that day which was Oct 15 or the day after. My periods have always been irregular and never really know when i am going to start but they are not usually this far off. We ended up fooling around but he didn't get to penetrate because he couldn't get and erection all the way again. I have read that you can get pregnant from "pre ejaculation", but it could be unlikely especially being that close to having my period, but i also don't know if he did anything during the time he was alone before I wen't back. It is now Oct 20th and i still haven't had my period, I am nauseous, more so after eating and at night, loss of appetite, and lower back ache and cant sleep. Can I be pregnant? I know we should have used a condom but I wasn't planning on anything happening.