I can't recall where I read it, but surgeries in the anal region can mess up your ability to control your bowels. Pregnancy--especially vaginal birth--is another thing that can stress and stretch out your control muscles in both the bladder and the anus. Your feeling like you constantly need to go, even when you have little, if anything to come out may be due to damaged nerves from those hemmroid surgeries. Which may be why the imodium isn't controling those "need to go" urges; it controls the intestines, but not the nerves.
Like Lil suggested, there are exercises that can help you regain some control of your sphincter. There should even be therapy places that teach these to you. The best person to ask about finding these therapists would be a gynocologist or someone who speacializes in or at least treats a lot of old people. Like I said, pregnant and post-pregnancy women often have this problem, as do older people. Exercise is probably not going to take away the urge to go, but it will at least help you hold it in. If you suspect that you may indeed have nerve damage from your hemmroid surgeries, try going to see another G.I. and tell him about your urges to go, even when you don't have a stool to pass, your past surgeries, your leakage, and the failure of imodium to stop the urge. I don't know if anyone has tried you on antispasmodics, but I think if the imodium doesn't work on the urge, the antispasmodics won't either; they are for keeping the intestines from spasaming and causing bowel movements. But it may be worth a try.
I read recently--I think on the health page on MSN--that they are starting to use botox injections on people with bladder control problems because it can make weak, loose muscles rigid and keep them from allowing leakage. If your doctor does suspect rectum damage, that may be something you want to try (I haven't heard that they are using it on rectums, but if they're using it on bladders...); at the very least it is numbing and it may help quell any overactive nerves down there.
And someone on this board some time ago said that her doctor was treating her for hemmroids, but at the last minute someone discovered that she actually had skin tags and that if they had been removed as hemmroids are, it would have been very, very bad for her. Makes one wonder about your reoccuring hemmroids when you were told they wouldn't come back and the fact that after the second surgery, you got messed up.