Welcome to middle age, my friend! I experienced the same thing (I am 44 with one six year old daughter). I think there may be a number of factors involved.
Here are some:
-"advanced" maternal age. Our body chemistry/collagen levels/hormonal levels, etc. are very different than they were at 30-something or 20-something, making recovery from pregnancy a different story than it would have been 10 or 15 years ago.
-I suffered from hyperemesis gravidarum during pregnancy, which essentially amounted to a state of starvation as far as my body was concerned, since I could not eat (resulting in increased stress hormones like cortisol). It is well known that body chemistry can permanently change under such conditions. Therefore, I now accumulate fat differently than I used to pre-pregnancy.
Such a state can be induced through severe dieting too...Eventually, the body becomes more "efficient" with its' intake of calories, as it attempts to offset the next period of "famine".
You can see how in evolutionary terms, the body's ability to do this would have helped humans through times of food shortage. Today, however, it can undermine our attempts at esthetic beauty. (and show us just how at odds with biology our attempts at esthetic beauty can sometimes be...)
-Genetics. What do other women you're related to look like after several births at your age? If they too have the same jelly roll, there's likely a genetic propensity to it that no amount of dieting or exercise will change.
In answer to your final question "What worked for you?", I'm afraid my best and only solution is to change your perception of your jelly roll: I can accept that my jelly roll is a badge of honor, that this is what I look like; and remember that it is a result of the best thing I have ever done (give birth to my daughter). Or I can spend the rest of my life trying to achieve an impossibility and feeling poorly about myself as a result.
It may help us all to remember that in other less vain cultures, the signs of motherhood, like jelly rolls and sagging breasts, are actually badges of honor that afford mothers certain privileges and respect that younger, still childless women do not get despite their esthetic beauty.
Good Luck!