Feel preg but negative test

Hi I had my period round the 6/4/11 then I bled again on the 16/4/11 then again a week later I'm not entirely sure what it means and it's more like spotting. My partner and I have a lot of unprotected sex but he hasn't fully ejaculated in me so I don't know how I could be pregnant but I sure feel it took to tests they were negative I'm not that worried or stressed about it just want to know exactly what is going on with my body