Hi R..
My name is S. and I'm going through a similar situation. I have 3 little ones - two girls, ages 4 and 6 and a 1 year old little boy. I had only had 2 periods after breastfeeding when what should have been a 3rd was late. I didn't think much of it at first, but after several days I decided to take a test. I BAWLED when it came out positive. It's been 2 months since I found out and I still get down about it.
I feel the same way you do - that God had other plans for me. The main reason I was so dissappointed is because I had a lot of plans I was really looking forward to for this coming year and am now missing out on a lot of much needed opportunities. It seems the world is passing me by as I sit home pregnant or with a newborn. I don't have anything to say that will make you feel better because nothing really makes me feel better yet. I just have a lot of faith and hope that when I see that little one on his or her birthday, I'll know this was right and he/she was meant to be part of our family. And, that missing out some things will be insignificant in 10 years, even though it hurts like hell right now.
Good luck! Don't be embarrassed - I always let people know my annoyance with being pregnant again and they turn into my cheerleaders. Just be honest - this was unexpected but you'll deal with it and so should they.