your stomach is specialized in processing plants, and plants alone. putting meat in your stomach strains it and makes it upset. however, you do have protection from poisonous plants you might accidentally have eaten.

eating meat can give you the poisoned condition, but you have advantage on saving throws against being poisoned as long as the poison is plant based. you also have resistance to poison damage if the poison is plant based.

amargatitians grow to about 10 to 14 feet tall, making them count as large.

you have an extra 5 foot range to all of your attacks, your carrying capacity is doubled, and you take up a 10x10 square as opposed to a 5x5 one

your sails are well over a foot long across the entire length of your back. this makes it awkward for someone to stab you from behind

all piercing attacks from behind you are at disadvantage

your tail is very long and slender, allowing you to use it like a whip. this natural weapon has all the properties of a whip and is affected by the proficiencies and mastery of whips along with martial arts. 

as an attack action you use your long tail to strike your opponent. this natural weapon acts like a whip and does 1d4+ your strength modifier in slashing damage. this attack has a range of 15 feet (this already takes the reach property of the whip, and the large species trait into account. do not add these to the reach of the attack)