Hi 1bi480g,
Thanks for your question. I don't have any experience with willow bark and hopefully others will be along shortly to lend their experience.
I can tell you it's important to check with the doctor before starting any new over-the-counter medication and/or "natural" dietary supplements. Even thought these supplement are marked natural" it doesn't mean they are always safe for everyone to take. Supplements can interact with medications and/or medical conditions we have.
On the aspirin, acetaminophen, ibuprofen question, again, it's a good idea to check with the doctor on what, when and how much to take of these medications - only a qualified doctor can recommend what's best for you!
Nancy