Aiyoh, gaining weight in first trimester is tricky because many of us kena morning sickness or nausea, right? Try eating smaller meals more frequently, a few of us found it easier to snack on calorie-dense stuff like peanut butter on toast, avocado, dates, or nuts rather than forcing down big meals. Make sure you're drinking enough too, sometimes dehydration makes the nausea worse. Since you're 13 weeks and your weight's not budging, best to check with your gynae or dietitian to make sure everything's okay and get a proper plan tailored for you, they can rule out any issues and maybe suggest supplements if needed!