My last pg was just like that. Honestly, I thought by the time my belly got big, it would "hit me." Then I thought, when my due date approaches, I'll "get it."
Honestly, even while I was being induced I STILL couldn't wrap my brain around the idea of having another newborn. It was such a weird adjustment for me. I've always been very "connected" to my babies from in the womb...thinking about them daily, but it was different with that pregnancy. The entire things was just so surreal. I felt bad about it after his birth and had to deal with that.
I do love him to pieces and now that he's 17 months old that's all just a memory, but it was very strange. For a while after he was born I wanted to have another baby just so I could do it "right" again. Then I pretty much got over that and hadn't planned on more kids and whammo - BFP.
Thankfully this time was different. Still shocked, but happy. I'm just having a tough time getting super excited until I see a really great u/s. Even then it will be day by day, but it's definitely better than last time.
So if you're anything like me, you may never wrap your head around it until much later, BUT it DOES work out. Don't be too hard on yourself about it. 
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