My gyna asked me not to gain weight/eat since 12 weeks pregnant.

Help! Hi Mummies. I'm currently in 21 weeks pregnancy, having my 3rd baby. I'm a plus size, in my early 40s and my first 2 children were born above 3 kg and healthy. I had GDM for my previous 2 pregnancies but cleared after delivery. Every checkup with my gynae, she will always remind me not to gain weight. Being pregnant, I will gain weight eventho I did walking, eating healthy, etc... I'm a SAHM with no helper and will walk to send and fetch my older children to their pr schools to and from home as well as other home activities/errands. Sometimes, my gynae will say don't eat and give advices like drinking all no sugar, which I followed. No fruits coz fruits have sugar but can drink coffee black, which I didn't take coz I believe coffee black is high in caffeine as compared to teas. So far, for every ultrasound checkup, my baby is doing well and healthy, just my weight. I will be taking the glucose test next week, similar to my previous pregnancies. When I ask what other exercise is safe and effective for loosing weight at pregnancy, I was advised to do just walking, which is my daily routine. Sometimes, I feel a bit sad, coz all the food that we eat contains a certain amount of sugar. If I can't snack on fruits when I have hunger pangs, I don't know what to eat. I cook for my family but sometimes feel sad remembering "no food" or "cannot gain weight". I've always thought if there is no weight gain, it's not a good sign for baby and mummy? I'm so confused and stressed at times. Any advice, please? Sorry for the lengthy post. Just need to pour it out 😩