sad or depressed?

Has anyone dealt with random sadness after giving birth without it really being considered PPD? My son is a week old and he makes me so happy but sometimes I just feel sad. I don't know why, I don't know what causes it but I just feel like I want to cry. I know I just had a baby so I'm hoping it's just my hormones being out of whack rather than going through PPD. I hate feeling this way and I've tried to tell my husband but I don't even have the words to explain why I feel sad.