My father has had dementia for at least 3 years. My mother passed from ALS in 2015 and he has just been getting worse. Anything I can do?

Geewiz makes excellent points. The behavior of people who have dementia is quite confusing and changing. It's not really something you can change yourself though. It's really something we have to adapt to, bend with and try to manage in order to keep them as comfortable and safe as possible. Gentle reminders may work for some, but, for others, they need direction and a steady lead to do everything.

If he's up a lot at night, I'd discuss it with his doctor, as a sleep aid might be explored. Crying out, making odd comments, repeating things, is not uncommon. Reading a lot and watching videos on You tube can provide ideas on how to distract or occupy their time. Sometimes activities, activity boards (some found online) can amuse them for a while. But, most activities require direct supervision and direction, so it can be quite time consuming. I know that my LO used to color, but, you had to stay right with her, because she would put it down in less than 1 minute, if someone wasn't with her, encouraging her to continue. 

But, as far as preventing the shouting or repeating.....I've never heard of way to stop that.  If he's overly anxious or agitated, medications might help, but, I'd discuss that with his doctor.  Sometimes, these are just a result of the brain damage and it comes in phases. For a while my LO repeated things A LOT. Then that stopped and now she can't carry on any conversation.  This progression took years, though. 

It sounds like he is living with you. If so, the best things you can do for both of you is to learn as much as you can about this disease and the best methods of working with your dad. There is a GREAT deal if information on the alzheimer's website about all types of dementia -- alzdotorg. AND there are many threads on this site offering techniques other caregivers have found successful. There are videos on youtube from Teena Snow offering best practices in working with those with dementia. And there are a variety of books that can help you better understand this disease. There are caregiving support groups you might attend --- often offered by United Way, houses of worship, hospitals and doctor's groups, and even nursing homes and memory care facilities. Learning as much as you can will help prepare you for his behaviors.
As to the bathroom issue --- Just bring him on a regular schedule. You really can't tell someone with dementia to do this action. Step over to him and gently say, come on Dad, it's time to go to the bathroom now. Help him up and bring him in.
This disease is frustrating in that behaviors constantly change as well as the person's ability so the caregiver is constantly challenged in how to handle things.
Good luck and visit us often, many here have 'been there and done that'. We learn from each other.