You need to add the line:
enabled=1
For example
[my]
name=My Repository
baseurl=http://yum.my.com/yum/my/
gpgcheck=0
enable=1
My repo's .repo file
[lamolabs]
name=LamoLabs Repo
baseurl=http://www.lamolabs.org/yum-repos/Fedora/14/$basearch
## gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY.lamolabs.org
gpgkey=http://www.lamolabs.org/yum-repos/RPM-GPG-KEY.lamolabs.org
enabled=1
gpgcheck=1
Additional things to do
createrepo
After you've setup a directory, shared it via HTTP, you'll need to run this command in each sub directory of the repo.
createrepo -dp .
I usually use a script like this:
destdir="/home/install_area/linux/yum-repos/Fedora/14"
for arch in i386 x86_64 noarch; do
  printf "\n\n==== creating repo: %-50s [%-s]\n" $destdir $arch
  pushd ${destdir}/${arch} >/dev/null 2>&1
  createrepo -dp .
  popd >/dev/null 2>&1
done
signing
Optionally you can sign your RPMs with this command:
find . -name "*.rpm" -print0 |xargs -0 rpm --resign
Also don't forget to import your RPM key into RPM:
rpm --import RPM-GPG-KEY.lamolabs.org