Could she be pregnant?

My wife and I are trying for a baby. I am just too curious right now so I had to get some opinions. We had sex just about the time of her ovulation. The only symptoms she is experiencing after about 13 days now is constant hunger and a bad cold and cough. It is time for her menses to start and she got an extremely light bleeding / spotting she says. She tried a home preg test couple of days ago which came out negative. She does feel tired and got lower back ache for 3 days in the mornings. What do you think? Are these symptoms because of the cold and cough she got or could she be pregnant? This discussion will definitely help me worry less!