I'm almost 12 weeks and have only gained one pound. I don't worry just because I know everyone is so different, but it definitely wouldn't hurt to talk to your doctor if you're concerned.
Im 9w ive been having a lot of morning sickness and been bringing a lot of my food up fingers crossed i will gain some weight thankyou :)
How far along are you? Check online for ideal weight for your height and age. Then if you are approaching 12 wks, you need to have gained at least 1 (up to 2) kg. 43 kg is rather low as a starting point. Perhaps you can ask if you need to have a blood test to see why you are not putting on weight? There could be underlying factors that could affect your baby later on. I don't want to alarm you but I've realised over these short few weeks how important food and weight is during pregnancy. Best of luck to you, I'm sure you will be ok.