Well, if you've got anyone who's had any kind of medical education; a nurse, heck, even a vet tech.
But if you're comfortable with it and have someone trustworthy enough, even just a family member or a friend - I don't know how they feel about your use of injections, but hey, it's worth a try.
If you don't know anyone who already knows how to do intramuscular shots, I would either inform them myself as my doctor informed me, or I'm sure there's videos on Youtube that explain proper procedure.
I'd be too lazy to drive to a clinic every other week, but maybe that's just me.