Prenatal Vitamins.... what if you cant take them?

ok, im 22 weeks. and ive tried Several types of prenatal vitamins....even flinestones. and they all make me sick. my doctor said i should be ok if i supplement many healthy food in my diet... well i eat a lot of tums... but i have a heard time keeping fruits and veggies down. my diet is literally limited to Pop tarts and hot pockets, and somtimes crackers...i know its strange... i wanna do well for my baby, and the doctor says its ok, but im worried he's going to have issues when hes born because of it. am i just worrying too much??