HCG is usually measured in IUs not mcg. Much like Insulin and GH are typically measured in IU.
Swale protocol states 250-500IU anywhere from twice weekly to EOD. HCG does not last long enough to inject only once a week. Not every doctor is an expert on the use of such drugs, in fact very very very few are. Heck, the majority still tell their patients to take ridiculous dosing protocols like 5000IU once a week; pretty much guaranteeing they destroy tons of Leydig cells casuing permanent damage.
If you're doctor said 500IU once a week, it would be better to do 250IU twice a week instead. It's the same amount per week but you are splitting it up and therefore getting a more steady level.