I believe you are right: Spreading Dogbane (Apocynum androsaemifolium)
Note the dogbane is because it is quite toxic and has killed dogs and other animals. Some people are sensitive to it and will get a severe rash just from touching it.
So tell us more. Where are you finding all these lovely wildflowers? And why don't you trust your own ID's, since you seem to be very knowledgeable?