Well, if you're looking to add shape/fullness to your butt and thighs, you're just looking to increase the muscular size of your thighs and glutes. 100 reps is far too high for this purpose. heavy-moderate weight is much more effective. With these sorts of dumbbells, you may have a problem making small increases, so it might be a good idea to factor in progressive overload by increasing volume first.
So for example, on each exercise you might want to start with 3 sets of 8 reps with one weight, resting for 1-2 minutes between sets. Then when you can manage that without too much of struggle, move up to 3 sets of 9 reps on that exercise. Then 3x10, 3x11 and so on, all the way up to 3 sets of 15.
When you can perform 3 sets of 15 with that weight, increase the weight by about 15% and start over with 3 sets of 8.
Ab work is totally up to you. Push-ups are predominantly a chest exercise, with triceps and front deltoids also involved. You can google ab exercises and you'll find all sorts, just pick and choose and these can be done with just bodyweight for high reps
Just remember that ab work will not burn fat off your stomach, since you can't spot-reduce fat. You lose fat by eating less calories than you burn. Might be harder because of your anti-depressants, but it'll still be possible!
As for a workout, you could for example train Monday, Wednesday, Friday. Monday and Wednesday would be weighted workouts and then Friday could be a bodyweight leg circuit. For example:
MONDAY
Dumbbell squats
Straight-legged deadlifts
Ab work
WEDNESDAY
Lunges
Glute bridges
Ab work
FRIDAY
Bodyweight circuit (example
https://www.youtube.com/watch?v=HIdxYCrqLQg)
If you wanna fit some general cardio in on another couple of days a week, go for it
There's also a fitness FAQ in this sub-forum for more information on dieting and so on.