Loki, why are you needing to change your bag at night? Is leaking a problem? Is your diet a factor? Trying to figure out what is going on with your bowels requires a bit of detective work. It takes a long time for your bowels to settle down after surgery - I mean years. But, it is possible to figure out how to manage them while they are adjusting to the shock of surgery.
First, I would keep track of exactly what you are eating, and see if you can spot a pattern. Are things worse on the days that you eat certain foods? Sometimes, the consequences of certain foods won't be seen for 2 days, so even more reason to keep a record. I find that my output is much higher if my fibre intake is high. And certain foods, like popcorn, can make it even higher.
Second, you mention taking Imodium as well as laxatives. That might be the culprit right there. It generally takes several hours for those meds to take effect, so I wonder if you're overdoing it on one, and then trying to compensate with the other. It might be worthwhile to go off the meds, and then gradually add the Imodium, to see if you can regulate your bowels better, using less, or just one of the 2 meds. This will be inconvenient, but it might help you find a better protocol. Even marshmallows (really!) can help thicken output. Again, don't overdo the marshmallows. Start with 2, in the morning.
Third, are you a beer drinker? I find that beer affects my bowels significantly, whereas wine and spirits don't. It's hard to turn down a pint of Guinness, but sometimes I have to choose the Merlot instead. Sigh.
Fourth, are you wearing the right appliance? Ostomy equipment companies are great at sending free samples - try them all, and see which one you like best. Are you wearing a convex flange? If not, try it - I didn't think I needed a convex flange, but as soon as I started wearing a flange with light convexity, my leaks stopped entirely.
And finally, as others have mentioned, irrigation may give you some freedom. If you have a colostomy, you are likely a candidate for it. Check the archives on this site for information, and there are plenty of YouTube videos as well. I don't irrigate very often, but if I am going out for the evening, I do. I know I will have the entire evening, and the next day free of bowel interruptions.
Apart from your ostomy issue is your sleep deprivation. See if you can find someone to help you with guided meditation for relaxation. Using this, you can actually train yourself to go back to sleep after you've had to get up in the middle of the night. It takes awhile to get the hang of it, but I use it all the time, (for myself as well as therapy clients) and it works. The more boring the guided meditation, the faster it will put you to sleep, so when you find one you like, don't switch it because it has become boring. You want boring.
Best to run all of these suggestions by your ostomy nurse, Loki. Of course, you can also talk to your surgeon, but I generally find that surgeons don't know anything about stoma management. But I'll bet you a pint (or a glass of Merlot) that your ostomy nurse will. Good luck.