With my first, I probably gained about 20 the first trimester, and it wasn't necessary. With my second, maybe 10? My guideline is the little weight gain in the first trimester is preferred, mainly because none of that weight is attributable to the baby. Once the pregnancy progresses beyond, it makes sense to gain more weight.
This time, my third, I have only gained about 3lb and am almost 12 weeks. I'm glad! But, I don't have the physical/hormonal need to eat something every two hours like I did with my first pregnancy, nor do I have nausea.
That said, I think if you are battling nausea, it's extremely difficult to NOT gain weight because eating frequently does help to reduce the nausea and something light like a salad doesn't really cut it. So, if you're feeling like crap and just trying to get through the day and finding that you're putting on pounds, I wouldn't worry about it at all. As you feel better, try to make good choices with what you eat and pay attention to what your body is saying. I feel like I've been more in tune with what my body needs and am trying to listen to that. Whether that has contributed to less weight gain this time, I don't know.
I personally find it a huge challenge to get exercise in during the tiring first trimester. I really hope I can get in gear in a couple of weeks when I should have more energy.