I feel for you because I have been there. My daughter has had the same problem. I will say this, the pediatrician is out to lunch on this issue. There is one easy one and one much more involved one. The easy one is pullups (I am convinced the chemicals make it worse). The walgreens version have less chemicals it seems.
The bigger issue, which is the real one, is the yeast in the gut which needs to be addressed. Yeast is usually either due to the use of an antibiotic which causes the yeast bacterial imbalence to be begin or due to gut inflammation stemming from food sensitivities. There are a host of things to do, but the number on thing is to get her on tons of proibotics (a broad spectrum such as one at your natural food store, culturelle -walgreens has - 1 a day). Get her off milk (go to rice milk and rice dream products) which will help with any inflamation. Consider removing the gluten (GFCF) in her diet as well as this can be tremendous improvment when inflamation is the cause (the antibiotics will sometimes cause clostridia which then screws up the system and both the yeast and the bacteria are out of control).
You can start reading on www.greatplainslaboratory.com. Also, in whole foods library, you can start looking at books on yeast overgrowth or food allergies, etc. You need to find a good preventative med doctor who will prescribe you Nystatin or another antifungal. Our doc in CA is awesome (www.drrachelwest.com) but may be better to get a local one. Your pediatrician can prescribe it and it can help immediately, as long as you accompany with proibotics.
Search for yeast overgrowth, there are products like ThreeLac (a type of priobotics) and Candicid Forte which are awesome and will need to be continued for some time. Yeast is tough to beat, but very possible.
We finally beat it wiht my daughter using homeopathy. We got a great homeopath in CA and I will be glad to share any other folks you may need. Just email and let me know.
J.