A., the very same thing happened to me. We had a little boy and a little girl, our son was 2 1/2 yrs and our daughter was almost 8 months. We only planned on 2 children and what could be more perfect that a boy and a girl?? Well, we were on a trip with my husband's family. I knew I was a little late, but I had not said anything to anyone and I was breastfeeding and I had only had 2 periods and they were not real regular, so I was SURE that I could not be pregnant. Anyways, we went to Wal-Mart and I secretly went and bought a test and stuck it in my purse. When we got back to my husband's grandparents, I ran to the bathroom and took the test (fully expecting a negative). I really was- but the test quickly lit up 2 bright lines. All of our family was outside barbecuing and I went to the door and called for my husband to come quickly. He could tell that something was going on, all I could do was hold up the test with 2 lines and just cry. We took a walk, it was a very quiet walk, both of us were speechless--, we just took turns reassuring each other that everything would be ok. We decided that we would not tell anyone yet, we had to get used to the news ourselves. Oh, yeah, did I mention, that after I had my daughter, I went to Weight Watchers, and I was only 7 pounds from my goal weight!! The thought of being pregnant and giving birth again was hard to accept. I couldn't quit crying. Our family knew something was up, they all thought that we were having an argument. We ended up telling his parents that night, and I just cried and cried. We ended up selling our 1200 s/q ft house and moving closer to my husband's work. Long story short, everything has turned out wonderful. Our son is now 4, and our girls are 2 1/2 and our baby is almost 1 yr old.
The first time I got pregnant I had a miscarriage. My sister in law also had a hard time getting pregnant, and there I was crying that I was pregnant again- I felt so guilty. That kind of put things in perspective for me. Just the thought of everything is really overwhelming. Our house is crazy, but I wouldn't have it any other way. My friends and family were also more supportive than I gave them credit for.
Bottom line, you need to get used to the idea itself and it may take a week or so. Work through it with your husband. We have learned that having 3 little ones so close in age, that it really brings you closer together, or it can tear you apart, you have to work hard to be a team to keep it together. If not, you will not be happy and neither will your marriage. I have learned to really work hard at my marriage. Something else with the 3rd is that I have truly enjoyed every minute- even the 2 am feedings!! :) With the first one you are a little nervous, with the second you were more relaxed, but so busy with the 2 to take time to enjoy. But with the 3rd, you already know that things will be crazy, and that you will be tired, so just enjoy it because having 2 others, you know how fast the time goes. Everything will be ok, it really will. Let me know how it goes for you. Best wishes!!