Hi, you could be pregnant as you had unprotected sex however you'll have to take a pregnancy test to know for sure.
The symptoms you are having can be signs of early pregnancy however you can get these with PMS too.
Sometimes worrying and stressing can make you believe that every twinge and ache is a sign you're pregnant and suddenly you believe you are.
Like I said there is a possibility and spotting in early pregnancy I'd also quite common. Since you think this may be a period even though it's light you should get an accurate result on a test by now... If a test is negative you should wait another week or so and take another test just to be sure.
Good luck...by the way nobody who ever went ahead with an unplanned pregnancy has ever regretted it...the love you feel for your child once it arrives overwhelms you and you forget any doubts you ever had...