Could it be that you have a high tolerance of THC so when you consume the marijuana in any shape or form by eating it that the acids in your stomach break it down to the point that there is nothing at all for your body to get a high from? Stomach acids are pretty heavy in the work that it has to do.
I could be wrong but that is the only thing I can think of, it seems the most logical explanation to it. Maybe you need to put more marijuana in what ever it is that you are cooking it with? Or you just need to get really dank bud, possibly do both!
But I could be very wrong