What Causes Frequent Urination And Blood In Urine?

I came of my period on the 26 december 2010, i had sex that night and also on the 28/29&30! i got a lump on the left side of my lower belly and cramps in the area. i keep needing to go for a pee, and today i noticed that i had a very light pink blood only when i went to the tolite and wiped. do you think i could be pregnant? even know i mite not of ovulated yet? im 16 years old and worried please help me x