constipation

I am extremely constipated ALL the time! Sometimes I don't go for 5-6 days. My stomach is huge. The doctor couldn't even see my left ovary in the ultra sound because she said I have too much bowel and gas. I think the prenatals are making it worse. Does anyone have any suggestions of what to do or is there any other prenatals that won't make me so bloated and constipated?