I didn't gain at all during my first trimester. I m currently 32 week pregnant
1week,vomiting,tiredness,my hubby laughed at me and said i was preg,now im 17weeks
I'm 29 weeks and haven't gained any weight. Actually lost a lot. This is my third pregnancy . With my first 2 I didn't start gaining anything until the end of my 6th month
I'm currently 38weeks and 5days with my second child and I started gaining a ton of weight right off the bat with her I was worried that it was too much I had gained 23lbs by 20weejs but then it tapered off just try and watch what your eating and your portions if you don't feel comfortable exercising
I'm also 7 weeks and have gained 3 lbs already. I'm constantly nauseous, so my diet has changed significantly to crackers and I think that's what's doing it for me. I have been exercising about 2 - 3 times per week but like you, I was much more active before I became pregnant. I found though that even riding a bike for 20 minutes helps my naseau and mood significantly, so maybe finding something light will help you stay active. Don't be scared of doing light exercise. Everyone I've talked to and everything I've read says even a short walk is beneficial!
Best of luck!