Feeling sadness

I am a second time mom and I never felt this way in my first pregnancy. I am not sad all of the time or even most of the time, but I’m getting waves of sudden sadness and I can’t pinpoint it! My toddler and husband are so amazing, we have no major stress in our lives: great jobs, beautiful home, supportive and local family and no financial stress. I’ll feel fine and happy and then all of the sudden get a sad feeling. I’m posting anonymously because I’m a little embarrassed for feeling this way. I will add I’m on Prozac for migraines. Is this a normal feeling? Can anyone relate?