You SHOULD speak with your doctor/diabetes specialist nurse/certified diabetes educator so that they can examine the area(s) in question, my friend.
The fat WILL return, but it MIGHT take, literally, years.
The same thing is LIKELY to happen to your thighs if you don't do enough injection site rotation.
The bruising is a reaction to YOUR incorrect injection technique. What's happening is that you are hitting small blood vessels (capillaries), which is causing them to bleed.
You do NOT need to change your insulins. You need to get your doctor/diabetes specialist nurse/certified diabetes educator to show you correct injection techniques.
I developed a slightly different condition, called lipohypertrophy, which means a build up of fat reserves in, and around, injection sites.
Since stopping injections in those areas of my abdomen I am getting rid of the lipohypertrophy, but this is more than 15 years later.