To be or not to be pregnant??

Angela • I have three wonderful boys I would love to have just one more, but I would like to take a break first before trying.
So my period is over a week late and I'm a little nervous because I recently had a baby he's now four months... I've had sex twice since he's been born after my six weeks. I took a pregnancy test a few days ago and it was negative. Could I still be pregnant? Should I take another test? Or go to the doctor?
​I am very fertile, I love my three boys but my husband knows that I'm not ready for another child. At least this soon.