Been feeling blue all day. Hubby helped lift me up when he got home, but I am just wondering if any…

Been feeling blue all day. Hubby helped lift me up when he got home, but I am just wondering if any other pregnant mama's ever have days when they feel down. There wasn't really a reason for my sadness, I just felt down for some reason. Does anyone know what causes this or how to help it? 37 weeks pregnant & FTM here.