TMI constipation problems... Help!

I am about 12 weeks pregnant with twins and am struggling so bad with constipation. I know constipation is already an issue with pregnancy but I also have to take 8 my of Zofran a day in order to function. I literally go for a week without going #2 and it's so uncomfortable. When it finally happens i have the worst cramping and diarrhea for an hour, not to mention the lovely hemorrhoid that come along with it :( I know it can't be healthy and I can't do this for another 6 months. What are some remedies that have worked for you? I've tried adding more fiber to my diet and taking Metamucil daily. I can't really exercise because of back problems but I'm willing to try anything else (safe) right now! Any help is greatly appreciated!!