You now have the reason, from the medical profession, so follow a program of improving the pelvic floor dysfunction: your doctor should have given you options to follow, if not, ask for a treatment plan.
I think you should really follow up your concerns with the frequency and volume of defecation with a doctor who would better understand the reasons. It sounds like you are not absorbing sufficient nutrition and this could could be for any number of reasons that we can't diagnose on forums, so again see a doctor to follow up the situation.
I'm 60 and have only had 1 colonoscopy during which they removed a few polyps. I would have gone for more except the medical profession where I live changed the rules and required all colonoscopies to be done in a hospital where they gather all patients together early in the morning and require them to wait for up to 4 hours before they get through the list sequentially and you have to make your way home. I can't tolerate this due to my Social Phobia, so have not been since, even though I should for my health. It was far more acceptable when it was done locally by appointment at the medical centre just around the corner from where I lived. It was a stupid money saving efficiency move and was counterproductive, in my opinion, in that it discouraged people from maintaining their health leading to greater future medical intervention effort.
Hasn't happened in my case and I have been experiencing bowel issues for more than a decade. Incontinence is more about weakening of the sphincters than the muscles in the bowel that expel the contents, I think, and if I recall correctly, the anal sphincters are often the last muscles to weaken in the body. However, if I don't evacuate soon after I get the urge, then the buildup could possibly leak, although I have only had a few minor occurrences of that when I didn't heed what my body wanted. We should listen to our bodies and when they want to operate, even though we can hold back a little for convenience.
People do vary in their digestion transit times: for me it takes about 3 days from in to out and I have noticed as I age that the flow is much more continuous, so after an evacuation it isn't long before I have more contents in the bowel (but I can wait a bit before it builds up enough to develop a sense of urgency to evacuate again).
Please, seek medical assistance for your concerns and follow what your body wants to do: don't force it and try to stop worrying so much about "what if": it's entirely possible your gut biome has degraded due to antibiotics and is no longer properly digesting food, hence the probiotic suggestion. I believe they can even do a fecal transplant (ie insert fecal material from a healthy person into your digestive tract) these days if things are too much out of whack, to restore balance. Let the medical profession worry about what it might be: your task is only to bring concerns to their attention.
