I didn't even know I was pregnant. I went to the doctor coz I was constipated and he said "Let's do a pregnancy test" I sat there staring at him thinking he was joking!! I had it bad from about four weeks till 12 weeks pregnant. I'm not sure what country you are in but if you go to a chemist and ask for something pregnancy safe they will be able to help u
if it has been that long you should really call your Dr. they may have you go in and get an enema.
My friend who is 23 weeks had the same problem her doc told her to take metamucil. It has worked great for her, she is able to go everyday now and it has never gave her diarreah or cramping. Also it worked within 24 hours for her.
Take some colace, its safe while pregnant and should produce a bowel movement in 3 days or less. Also you might want to change prenatals some can really mess up your bowels.