Help the prenatals are making me super sick!?

hey everyone im 14 weeks pregnant.. when i found out that i was pregnant at 4 weeks i bought over the counter prenatals, natures bounty prenatals and i have no reaction towards them.. when i went to my doc he gave me duet dha and i cant keep them down.. he told me to just take the natures bounty until my second trimester.. im in my second trimester and ive tried taking the prescription samples hes given me and it gives me the worst upset stomach! he says my baby needs the dha.. i dont know what to do :( help please