Tummy getting softer not more tone ?
This same thing happened to a friend of mine. She did crunches and planks, and side this and twist that . And she kept getting plumper around the middle to the point people thought she was pregnant.
This is because all that crap works out your ab muscles...when you work out muscles they grow. When muscles grow under fat...they push the fat out and makes that "grow" as well.
Point is...when you want to tone ANYTHING...lift heavy and get a good burn going, that gets the process started. The main factor is, of course, again, Nutrition. You have to be mindful of what you're putting in if you want the results on the outside.
Research, my dear...research.
Best of luck.