I am in a very similar situation. My children are much more spread out, but since the birth of my son in Oct 2000 I have not been able to lose any weight. I have actually gained about 15-20lbs. I feel huge. I have all of the same problems you have described as far as stretch marks and the under the belly (awful) thing. I notice and dislike all of these things now, I can't imagine what it will be like if I do shed all of this weight. I don't have an answer to the problems, but I am sure some exersize that includes weight training for these specific areas can help some.

Rosie