Oh the dreaded face of pregnancy weight gain. I gained 60lbs with my first and it was horrible. I took everyone literally when they said I was eating for two and ate for 2...sumo wrestlers. Then my daughter was born and I hardly lost 8 lbs. I was devastated. It took me a year to lose it all. When we had our second I was determined to not gain as much and stayed with in the 30lbs alotted me. But I stressed over every morsal I put into my mouth and felt guilty for being hungry - I ate but my attitude was unhealthy. Still, after her birth I had a long road to lose the weight I'd gained. It did happen, but each time I worried and fretted about it, and someone said "Oh, you'll lose it" I wanted to bop them in the kisser. It's easier said than done. I learned though, that neither pregnancy had the healthiest attitude. The first time I was glutonous and that did me no good, but the stress and worry the second time wasn't much better. It wasn't until the 6 month mark when I made up my mind to be health focused not number focused did I relax.
That being said, you can and will lose it! You've taken good care of your body since having your second and so your body will once again work with you to lose the weight after this baby. You know, after your first pregnancy how to manage what you eat and what is within your control, but remember you're growing another person. That takes time, energy and fuel, remember the weight that you gain is fuel and protection for your little one. It is also a HUGE sacrifice that you're making, of your body and your self esteem. No matter what you feel like remember that you're beautiful. The fact that you're showing sooner is attributed to the fact that you are on babe #3, not because you're gaining too much.
Hang in there. I know it's hard to face the weight battle. We can thank society for our insecurities and fears. Just remember when it's all said and done, you'll have a sweet baby in arms and you will lose the weight. And what I've hung onto, is with all my struggle to be healthy and lose weight, I'm teaching my children to keep their bodies healthy all the time (we don't talk about weight loss or diets, just healthy bodies so that we are there for our families.). This is a chance to show them how to keep care of themselves, because you're doing it too!
Good luck and congratulations!