Depression

Is feeling depressed normal at 28 weeks? I didn't feel it at all until about a week ago I feel really sad all the time. And I feel depressed about how my life is changing and how I am always alone. I'm not sad about being a mom or anything I'm just I don't know extremely sad about how different things are going to be. I am not more motivated to do anything if it involves doing something just for myself I can't seem to leave the house to make myself happy. And I don't know how to shake the feeling.