Tc, the symptoms you mention of feeling that there's more to come after you've had a bowel movement but you just can't pass it, having a little bit ready to come out that you discover when you need to go for a wee & the fairly recent change to needing to pass stools several times a day, sound as though to do with incomplete evacuation. As Sparkle says this can be a consequence of prolapse & can also sometimes come with other conditions. Any change in bowel function that goes on for more than a few weeks needs checking out as we all know, so you're wise to have the colonoscopy in the pipeline (excuse pun!) That should help identify what's going on, so please make sure you describe graphically as you have here, what happens, as this will help them help you. They hear that sort of thing day in day out so will not bat an eyelid!
Pelvic floor exercises can help with incomplete emptying - the muscles act as a sort of hammock supporting the pelvic organs & that includes the rectum. So when the pelvic floor weakens as a result of hormonal decline & ageing it's not only bladder & vaginal areas that can be affected. If you haven't had pelvic floor physio, this is well worth asking about - a specialist physio can help make sure pelvic floor exercises are being done correctly & these can be enough to get the area functioning better without the need for surgery. They need to be done a few times every day, but once in the habit they become a way of life. For anyone new to them it's worth saying that they need persistence at first as it can be slow to see results, but they really do work & help bladder, bowel & sexual function. Win, win
Might be worth experimenting with diet too if you think more fibre (& fluid) might help to produce a bulkier stool which may be easier to pass completely, i.e. without that uncomfortable feeling of there being more to come. Or supplementing with something like psyllium husks, as I think was mentioned earlier (mixed into juice & water to disguise the taste!) or Fybogel. Ground flax seeds can also help bulk things up & speed transit, but if you have problems with inflammation their high fat content may not be ideal. As you have inflammation, I'm loathe to suggest probiotics as they may make things worse, but personally I've found these helpful for gastritis & slow transit.
As Sparkle says, exercise can really help - I find both an exercise bike with cross trainer handle bars & a rowing machine give the abdominal & pelvic area a good workout that improves abdo muscle tone & helps to keep things moving in the right direction!
Unfortunately I can't find this morning a very helpful link to a comprehensive pelvic floor website that goes into detail about how the bowel can be affected. But the following gives an outline:-
https://www.oxfordgi.co.uk/obstructed-defecation.
I hope the colonscopy helps put your mind at rest & that you find something that helps you feel more comfortable.