Worried I might have PPD...

I had my LO 8 days ago and i couldnt have been happier, but for the past 2-3 days (since my hubby went back to work) I've just felt sad like all the time...ill burst into tears over nothing and when i look at my baby I'm happy but i feel sad i think too... I'm just worried, i love them both more than anything and i have no reason to be sad so i dont understand why i feel this way. Once hes back home tho i feel fine, still not 100% but better than when I'm alone. Is this PPD?