Can I be pregnant this soon after giving birth?

My son is 9 weeks old and I started getting my period again at 7 weeks postpartum. I had a little over a week ago and today I felt a little dizzy and spotted a little. Now I have a headache and I'm getting congested. This feels a lot like when I got pregnant with my first. Could it really happen this soon? We used protection but not till the end. Is there a chance I'm pregnant?