I Am 36 Weeks Pregnant. Had Just 4-5 Bites Of

I am 36 weeks pregnant. Had just 4-5 bites of watermelon at around 8 pm and noticed burning sensation in stomach after 9 pm. Then i had an anti acid at 10 pm. After half an hour , i.e. around 10.30 i had duvadilan and multivitamin which i take daily prescribed by my gynaecologist. After half and hour of that i vomitted twice a lot of purple colored fluid. What is the cause of that? I am not allergic to either watermelon or any of the medication taken.