Period 7 weeks ago, feeling pregnant?

I have a six month old boy who I have been mostly breastfeeding. He also eats strained veggies, juice, cereal, occassionally formula, and water sometimes. I had my period about 7 weeks ago and I feel pregnant but I took a test that came out negative. I have been sexually active but used condoms not birth control. What is going on? Could I be pregnant? Was the test faulty?