Hi D. (love your name),
Something that works for me (when I think to do it) is pretty easy and effective....it comes from pilates and another exercise program I used....what you do is tighten your stomach muscles, like your sucking it in, but imagine your trying to get your belly button to touch your spine...for some reason, that makes it feel different for me, like the bottom abdomen is being effected.
While your doing this, make sure you are exhaling (through the nose). Hold it for about 10 seconds, release for about 10 seconds.
You can do this lying with your back on the floor with your knees bent or with your calves resting on the seat of a chair (that's what was suggested to me). You can also do this during regular exercise and what I've found when I do, is it gives me a little extra stamina...immediately! It's strengthens your core.
I do it sitting at my desk a work, too. While I'm sitting and working, I'm also trying to get my belly button to touch my spine!
Hope this helps. Good Luck!