When I was younger I have always had a booty now for some reason I am a hundred pounds smaller and I have no but it is flat I don't know what to do help

Well, you could get a Brazilian butt lift.

I used to also. Now I have an innie instead of an outie. It's concave.

I don't have much of a butt left either. I'm ok with that! Except it hurts sitting for too long. 

Build muscles, get a pillow and enjoy being able to wear smaller clothes.  Congratulations on having that much wt loss!

Seems my butt also went away. If only I could transplant some of my bat wings to feel in my butt cheeks!

I have found that taking pictures, then looking at them by cropping off my head - so I don't know it's me- has helped me understand my new body.  Looking objectively and honestly, you might see something different about your new proportions and something you like instead of your old butt. 

Let's hear it for the collarbones!!

This is an opportunity NOT a set back. Why, because now you dont have a lot of excess fat covering your glute and upper hamstring. So when you do exercises to strengthen your glute and upper hamstrings, it is going to look like firm, strong muscles rather than a bigger pile of fat.

My personal trainer has me doing these excerises

1) one legged cable kick backs (see a video I found here) http://www.bodybuilding.com/exercises/detail/view/name/one-l egged-cable-kickback

2) squats

3) squat jumps (squat..then from the squatting position explode into the highest/tallest jump you can...also works the calves)

4) one legged squats (for when the squatting gets to easy) 

5) lunges

You can use just your body weight for all exercises.

When you find they get too easy, for excesises 1, 2 & 5 you can use ever increasing weight by using handweights or barbbells.

DO NOT use handweights or barbells for squat jumps or one legged squats. Any deviation in form, with added weight you can REALLY hurt yourself. Be SAFE.

If the squat jumps get too easy change it into a low squat, then jump forward as far as you can, squat, jump back.

Be safe!

But really, you are in a position RIGHT NOW that lots of body builders would KILL to be in, in the sense you ahve little body fat covering those muscle groups so you can build them into something really amazing.

This is a great opportunity!

"for some reason" the reason is because some of the 100# you have lost came from the fat you had in your butt. 

I just spit my coffee across my screen.