Had unprotected sex about a month ago started the day after was only four days instead of my usual six and really light now I'm spotting for three days my body feels off my boobs feel huge I'm tired all the time and I'm nauseated off and on

From research I have seen, yes you could be. But I have also had all of those symptoms a long time ago when I was scared that I could be pregnant. Your body is a very interesting thing and if you mentally believe you could be pregnant and are worried all of the time, you could be making your body show symptoms even if your not. If I worry a lot then I have lighter or late periods, and I have been told by my doctor that this is normal for women under stress. I would say calm down and relax for a while and then take a test when it has been long enough just to be sure.