Could I possibly be pregnant?

I had sex on April 29th, 2011, May 31st, and June 2nd. In that time my 'period' (Or what I think could of been my period) has come (going backwards) June 11th (Should of come June 8th and was black, and very short [1 1/2 days]), May 14th, and April 16th (both a couple days late and very light, dark brownish and only lasted a day, didn't even fill up a sanitary pad). I have a 28 day cycle and a 12 day lutheal phase. Is there a chance I'm pregnant?