My first inclination would be to suspect the butter, because I used to eat
lots of dairy products and didn't suspect they were a problem for me until I
eliminated them at an excellent doctor's suggestion and tried reintroducing
them months later with negative results. Also, I've noticed that many
(though not all) of the people in this and other low carb forums who
continue to have symptoms eat dairy products. It's one of the first things I
ask low carbers about who are having problems, since so many think dairy or
raw dairy is fine and assume it is not hurting them. However, what caused my
problems may not be causing yours and I am no diagnostician. Plus it's
difficult for anyone to diagnose without seeing you or running tests.

As for doctors, I try to find osteopaths or functional medicine
practitioners, who are few and far between. When that fails I ask around to
see if anyone knows a doctor who is at least prevention-oriented and not
quick to recommend drugs or surgery. I got lucky once when I asked the
health insurance operator if any of the docs practiced any complementary
medicine and got directed to the best doctor of my life so far (a general
practitioner from Russia and Israel whose office included an acupuncturist).
You can also do things like look to see if any of the private medical
offices in your area advertise complementary therapies, which is suggestive
that they may take things like diet and food intolerances into account. If
that fails then I just go and hope for a good one. We definitely do need
more public info about our doctors.

One thing to watch out for is recommendations to buy expensive supplements
or pay big bucks for bizarre treatments like foot baths with metal rods to
extract "toxins" and the like.