perpetually constipated

ok so i am 26/f. about a year ago i had a back injury that kept me in bed for about a month. and took until now to heal.
ever since i have had extreme constipation issues. i eat fiber, drink water...but still just cant go. the problem is that i do not get the urge to anymore. ive been to the doctor, and feels there is no need for sigmoid/colonoscopy....and gave me lactulose to take.....this does work, but i have to stay on top of it. but i mean, im young! i should not have to take something to defecate. i used to be very active, but after my injury i stopped exercising regularly...i also used amphetamines a lot in my college years....and have completely stopped 2 years ago. what is going on? help!

[Jaybay]

Were you taking narcotic pain medications for your back injury?  That alone will slow down your colon quite a bit.  Some people also have naturally slow transit time.  Once a day is normal for some; every three days is normal for others.  

Your body has been through an awful lot in the past year, so it's not surprising your colon has gone on strike a bit.  Age has nothing to do with it.  Your body needs a bit of help with the lactulose for now, so keep taking it.  As you're able to get more active you'll probably find you need it less and less over time.