Amitriptyline is very effective in helping a person fall asleep faster. It has done that for me. I understand staying on it, even just for that reason.
If you're taking laxatives twice a week most weeks, then I would suggest you taking a lower dose of laxative daily. Perhaps you've been told that, if you poop good every 3 days, that's sufficient. I'm a nurse, and that's what they used to tell us. We would only give a laxative, if a patient went 3 days without pooping a good poop. Following that protocol, I used to end up giving enemas and manually removing hardened stool. It's obsolete advice.
I believe chronic constipation led to my diverticulitis. I decided to do whatever it took to make myself poop a good amount every single day. It has changed my life for the better. That is the way our bodies are supposed to work. I use polyethylene glycol powder, sold as MiraLAX and as generic brands - all exactly the same. It is an osmotic laxative, rather than a stimulant. Osmotics are the best. They hold water in the stool, just as dietary fiber does . . . only they are more reliable. Stimulants, like senna, irritate the lining of your colon. Not the best thing to do. Stool softeners, like Colace, will make stool less hard, but they are inadequate. They produce stool with a putty-like consistency. Not what you're shooting for.
Being a powder, you can easily experiment and learn how much you need. I take it first thing in the morning mixed with hot chocolate or hot tea. I now poop normal every day, even though I take hydrocodone twice daily.
If I wasn't able to afford polyethylene glycol, I would use milk of magnesia - also an osmotic agent, but real cheap to buy. If you're only having a good poop every 3 days, you need to revise your program because you are harming your colon by allowing too much pressure to keep building up. You can get away with that for years. Then, one day, you discover your colon is damaged, when you're in the emergency room with the intense pain of diverticulitis.