I think I might be pregnant

I think I might be pregnant I started my period on 4/3/08 and was off on 4/7 my boyfried and I had sex on the 10,12,14,19,20,21,26,27 and now I boob are tender and has been since the 20th of this month (normal my boobs dont start getting tender until a week before my periods comes) also when I sleep at night I cant sleep on my tummy becuase of my boobs and in the morning I have sharp pain on the left said of my tummy for like the last past two days but only in the morning so how big of a chance might I be pregnant, I usaully always get my period on the first of the month or on the 3rd of the month

P.S my 14th day would have been on the 20th and my 28th day would have been on the 4th of may but I get my period also no matter what on the 1st and on the 3 rd and yes I know that I should of used protection but my boyfriend and I have been having sex since I was 17 and I have NEVER!!! worry about being pregnant and I am now 20