Okay, so you have something a little different to me (it is very rare that anybody with CD will get the same surgery as me) but most of the things you can do are similar. Before I forget there is a very long thread on ileostomy reversal here, you might find some additional helpful information there.
High output is often treated with drugs, the most common being loperamide (aka imodium), lomotil or codeine. You need to speak with your medical team before taking any of these but they can certainly help (and you should get them on prescription).
I didn't want to take medication so I bought some psyllium husk capsules and took a couple of these before meals. Psyllium husk is a bulk forming laxative. I know, you now think I'm bonkers for taking a laxative but trust me on this psyllium husk works by thickening the stool and slowing down the transit through the gut. I used it for the first couple of years but rarely bother now (my surgery was 10 years ago). While you can buy this over the counter I would ask my medical team about using this first due to the nature of Crohns disease.
The things you eat can make a big difference, many foods will go through you like a dose of salts whereas others will slow things down. Finding out what works for you can be a bit of an experiment but typically white starchy foods are good, leafy fibrous foods not so good. So increase your intake of things like pasta, rice, mashed potato and cut down on the lettuce. Some foods will make you sore - when you're going 15+ times a day that's almost unavoidable anyway, a good barrier cream will make you feel much better, I used Sudocrem but these seem to be very individual so you might need to experiment. There are some really useful dietary tips on this page. Remember too that any dietary changes should only be temporary, eventually you should be able to eat anything you like.
Another thing to do is not give in to the urge to empty your bowels straight away, try to hold on for a few minutes and then go. Increase how long you hold on for slowly day by day. There comes a point when you can hold on so long that you stop worrying about toilets and life gets much easier then. You'll also find if you can occupy your mind you'll need to loo less often, I noticed this when I went back to work.
Keep on at the hospital, too many of them neglect after care in these cases so you really do have to give them hell, the stoma care nurse is always a good place to start.
HTH
Bellavita's other/better half