Pineapple for pregnant

Im n a bad situation during my first trimester. i vomited everyday even without food or drinks. spotting and cramps. My gynae ask me to eat anything and drink anything except of alcohol, smoking and pinneapple. He mention that there is a substance in pineapple that will trigger slight cramps and it will not be good for my case. OTher food like watermelon, grass jelly etc are all ok