My mother became pregnant with my youngest sister after she and my father were very satisfied with the family structure (2 boys, 2 girls). I know it took my mom a while to make peace with the pregnancy, but it quickly became apparent that we weren't complete without her. She's the only child at home now, and she and my mother are very close. It may not be clear now why you are pregnant again, but it may become very clear in the future. It doesn't make you a bad person to feel disappointed, sad, or frustrated. They're just feelings. I hope your pregnancy goes well, and the reason for the unexpected addition becomes clear. Best wishes!
Im having a similar issue. I am getting married next weekend and thought i was late due to stressing. I took a test to stop my fiance from worrying and now im worried because it came back positive. Not what i want right now
Don't worry, it's a perfectly normal feeling! Maybe speak to your Dr and they can put you in touch with someone to talk to about it? X