When should we start to see weight gain and start tracking?

I lost 3 kg in tri 1, didn't gain in tri 2 even tho my appetite came bck. But gained close to 12kg frm 3rd tri onwards! My gynae was even asking me to watch my diet as baby was big but I just cldnt help it 😅Didn't have GD but baby was 3.8kg at birth.