Don't worry about your weight gain :) it's a good thing that you haven't lost your appetite as some others have especially in the first trimester. Just eat in moderation and try to add in or swap some food for healthier options :) also, light exercise or walking is completely fine throughout pregnancy, helps with blood circulation to baby. Just not vigorous and heavy exercise especially if you're not used to it.
Don't try to lose weight at this period. It's ok to gain any amount of weight as long as your pregnancy is normal. You will lose weight if morning sickness starts. Eat moderately and always remember not to eat for 2 even though you're pregnant.