Can your ovulation change?

Kay

If this idnt allowed in here I'll delete it. I was wondering if your ovulation can change? I was supposed to ovulate on August 20th. Today is the 24th. I had unprotected sex on August 13th. my period isn't due for almost 2 weeks and in having all the symptoms of being pregnent. nausea, occasional vomiting, discharge, lower back cramps, sore boobs, hormonal as one can be. I didn't think you can get pregnent a week before ovulation.