Definitely don't worry if your doctor hasn't said anything.
I started a pre-baby diet on my OB's advice about six months before we officially started trying (I have health problems, so we wanted to take our time). I gained more then than I did since the pregnancy started! Seriously, I went from a healthy 150 for my body shape to 200 lbs, but I didn't really look heavier. It was all in adding more protein and storing more healthy fat, I guess.
Since I got pregnant, I gained NO weight until my 21 week appointment. That scale was stuck at 200 half my pregnancy and I asked every time if that was okay. (I wasn't exactly complaining, I already sort of felt like I gained 50lbs.) The doctor said my body was just going to use what it had at the start of the pregnancy and as long as I was still eating healthy foods and staying moderately active, I would be fine.
At my last appointment, I weighed in at a whopping 206. I thought, "Oh good! I gained a little!" The doctor said she had hoped I would LOSE weight! So, now I'm back to being more careful with my diet.
Talk it out with your doctor, because everyone is different and what is "good" for some people may not work for you.