Hi OP, I’m 19 weeks. My first trimester was horrendous as I was so sick, weeks 6-10 were basically me barely eating and having massive food aversions. I lost about 5lbs from that. But then weeks 10-13 although I still felt sick and was still being sick, for some reason if I didn’t eat something heavy and carby every 2 hours, I would get so nauseous and throw up so I spent weeks 10-13 basically eating constant, carby shite which was really distressing for me as I tend to watch my weight/ figure usually. I put on the weight I’d lost plus 3lbs in those few weeks 
That went about 13/14 weeks and now for the last month I’ve been back to eating healthily/ normally with the odd treats here and there. I’ve also been able to exercise more due to feeling better so have now dropped about 4lbs and plan to try and just maintain what I can now and accept that I’ll be putting on a bit of baby weight. Baby weight I can take, but not piling on a load of weight in general.
I usually eat about 1250-1400 cals a day and am still eating that and plan to continue to until the 3rd trimester when ill up it by 200 (my midwife said you only need an extra 200 cals in the 3rd trimester) I hope by doing this and continuing the exercise, I’ll put on the least amount possible but honestly who knows.
I find it hard to have a balanced discussion with anyone IRL re this as people tend to get hysterical and ‘but you’re having a BABY, you HAVE to put on weight, you must eat as much as you can’ blah blah. I’m certainly not restricting myself but I’m being sensible because quite frankly I’m vein and like being slim!!
If you do a desk job then I don’t think you need to be eating anymore than 1200-1500 cals a day personally (depending on how much exercise you do obviously)