I'm pregnant and so extremely overjoyed and depressed at the same time...Could it be hormonal?

I am 26 weeks pregnant, and lately i've been having a few meltdowns. I will begin sobbing for no reason that i can think of and utter sadness comes over me. I don't really know why because I cannot wait to meet my little bundle of joy, and have a great life. Married to a great man, we both have really decent jobs, love of family and friends...a great little life! I did recently change jobs to prepare for our baby, and I'm feeling more bored than usual as this job isn't too demanding. I feel like all i do is work, sleep and wait for our baby. I feel so depressed sometimes, but I cannot think of a single reason why i should be...is it hormones, too little mental stimulation, depression, what??? Any soon-to-be moms feel similar?