Prenatal importance??

Question... How important is taking prenatal? I’m 18 weeks and I have not taken mine in about 3 weeks. My prenatals are so huge and i throw up every time I take one. I have lasted a long time despite how hard it was but not it’s unbearable. I was so constipated while taking them that I had to take laxative (which I was not comfortable doing being it is dangerous) but my doctor said there was no other solution. My insurance doesn’t cover the gummies and the man at the pharmacy said over the counter gummies don’t have folic acid in it. Can I just take folic acid? Btw in the last 3 weeks I have been able to move a bowel regularly. I took one this morning have been constipated all day.