Why does my baby move when i eat?

everytime i eat the baby starts kicking like crazy! yesterday i felt 15 kicks in less than 3 minutes. the baby is VERY active. Im about to be 20 weeks and im not thin. Why is it i can feel the baby so much? the ultrasound tech also said the baby is very long. could i be carrying a large baby? Im 5'1 and my husband is 6'1.