Hi, I have a 2 year old mini daschund. He is potty trained, eats once in the morning and once in the evvening. The last feeding is usually around 6:30. I always take him out before bed. For the past 2 months he has been waking up EVERY night between 2-4am crying and whining to go out. I think this is a bad habit he has created and I don't know how to break it! Can anyone help me please?? I haven't slept through the night in 2 months!

There are several things you can do.

Why not start taking up his water after his evening meal at 6:30.

It is possible that he has a health problem or perhaps, there is an animal outside making noise in the middle of the night and he wants to go out.

After his evening walk, you can take him to your bedroom and block him in and turn on a fan for background noise. Perhaps, if it isn't an animal, he will sleep through the night.

Last resort, consult a vet.

No, the first step for any change in behavior is a vet check explaining the problem. You can't train a physical problem away. Is he neutered? It could also relate to him deciding he is a big boy now as he approaches maturity at 3 years old.

Try making him walk around more when you take him out. Exercise stimulates the body to eliminate. The other side of that coin is crating him if you haven't been. If he is free to prowl around if something wakes him up, he may stimulate himself to need to relieve himself. A dog that has not been crated since it was little, may take some work.
Start just putting its toys and treats in the crate. Praise it for going
in. Feed it in the crate. This is also an easy way to maintain order at
Feeding time for more than one dog.

The "shut the puppy in a safe room" is a fallacy. Very few houses even have a
Safe room. How many of us have a room with a hard surfaced floor and nothing
Else? Most rooms have electrical cords to chew if nothing else. In addition
To destroying anything a bored puppy finds to chew, it may choke or have
Intestinal blockage from the pieces. I had a friend that left her dog in a
"safe" room. It ate a hole in the floor covering. The safe rooms fail to
Give the dog the comfort of the enclosed space their instinct requires. Nor
Do they restrict activity extending the time the dog can go without relieving
Itself.