Workout and still too skinny?

Yes, your workout is flawed, because you have been doing the same exact exercises repeatedly, your body has adapted to it and you won't be gaining any extra muscle. A technique to change this is called "muscle confusion" which is by making your body change how it feels the exercise. This can be done by say doing crunches on a decline bench, this changes your technique and is a drastic change to a workout and you will continue to gain more muscle. Also try and do more than just body exercises. Go towards weights also.