Congratulations on second baby eyelash!
I can understand your concern as I was worried about weight gain more so with my first as I didn't know what to expect weight wise and I was terrified of getting stretch marks.
For my first (now 21mths) I weighed 9 stone. I felt that my normal weight for 5'6" should be 8st 7lbs and went up to 10.5. (I was 8.10 4 wks post baby). For my second (now 8mths), I weighed 8.2 and again went up to 10.5 (I got down to pre-preg weight in 3 wks because I learnt what worked). I did find though that my second preg showed earlier because tummy muscles are looser.
I read in a book "Pregnancy" by Malcolm Gillard that if you keep your weight down to a sensible weight, you have less chance of high blood pressure and definitely won't have stretch marks. I felt this was good, honest advice rather than people saying "eat whatever you want, when you want". So I ate sensibly, I cut out butter, sauce on veg and meat/fish, on salads I only had lemon juice/balsamic vinegar with a teeny bit of dressing (always asked for dressing on the side), I became puffy faced the next day with: smoked salmon, bacon, cheese so I cut those out. If I was at a party and cheese presented itself, allowed myself one bite and savoured it as really I could eat cheese until the cows came home! I don't eat chips, potatoes, bread, rice, pasta as a rule anyway but if I was so hungry in the morning I would allow myself toast which did set me up for the day. Rice cakes were fab if I needed the carb. I found egg white omelettes with veg fabulous. If I ordered chicken ceasar salad, I would have it without crutons and cheese which saved getting puffy and calories. I had choc and pudding once or twice a week and that meant I didn't feel deprived. So if you do low fat and low sugar you can still nourish your body and not feel weak/ill but will cut out the unnecessary calories.
Oh! When I needed to nibble I ate: baby tomatoes from M & S, baby gems, baby veg which is low cal and delicious, fruit such as mango (big bowl from serve yourself section in Sainsburys where you can choose the ripe bits). I found this really helped.
Forget the word diet and instead think "eat sensibly". If you cut anything out of your daily regime, promise it to yourself post preg when you will be lighter anyway.
Good luck!