Sucks about
your shoulder injury. Hope surgery will fix it up for you.
Lomotil won't control your UC. So, that's not a med that would have helped you...just bms quality/consistency and spasming.
you weren't on any rectal meds....for maintenance.
But considering you had serious injury, i would assume that tipped you in more favour of a flare.
As well, your preoccupation with the injury can have you neglecting some symptoms of a flare starting.
No use in wondering the why....just concern yourself with the what you can do to deal with it as early as possible.
Feel better soon,
q