Scared

So I am suppose to start my period on the 1st of January but I didn't. I have always had an irregular period ever since I started menstrating. I am also sick and have a big trip coming up so I'm stressing hardcore about it. The last time I had sex was about a week ago on a non ovulating week with a condom. I guess I'm wondering is it due to stress that I haven't started and that I am sick or should I go to the doctor to see if I'm pregnant (I also have had terrible cramps and my breasts hurt like they usually do). Please give your opinion. Thank you