could I be pregnant

My cycle length is between 25-28 days it switches up at times. I use the calendar and it is pretty much correct maybe a day or 2 off. I have my period from 14-19 of this month. I had unprotected sex 21-23, 27-28. I just happened to look at the calendar because I was feeling nauseous on the 22nd and on the 24th. I know that it was way too early to start feeling symptoms for pregnancy. on the 29th and today I've been having a lot of interjection and gas. My stomach been making a lot of weird noises today and a little uncomfortable feeling. When will be the earliest I can test? When do you start having pregnancy symptoms?