K., I can't assure you that you won't gain more weight this time, it's entirely possible. Mostly because stuff isn't quite as tight after the first one, ligaments that hold the uterous elongate, and so you might carry the 2nd baby lower. I personally felt as if I had an anvel wedged in my pelvis with the second baby, lol. I will stress that eating properly and cutting out wasteful calories (deserts) will help you with this emensely. Also regular excercise, even if it's just an evening walk around the block will help beat the pounds. I gained 60 lbs with my first child, and it took me a year to get it all off. I only gained 40 with my second child and I was able to get off all but 8 lbs of it. I am not talking about what happened when I had my son at the age of 32....LOL. Still, be encouraged that eating healthy and staying active goes along way toward not becoming a cow.
As far as showing this early, being your second, it's normal. Mentioning your concern at your next office visit might get you a sonogram to check the age of the baby, sometimes if your dates are off a bit, it makes a difference.