that sounds about right. last year when i had my 5th concussion, 3rd Level III, i was told not to ski or participate in contact sports for 4-6 weeks. after your first concussion you are much more likely to continually get them after even minor falls, blows to the head, etc... it sucks. i got my first one in 5th grade, then 7th grade twice, then 9th grade, freshman year of college, and then sr year.
listen to the physician, though. and follow up with your PCP in a two weeks to see if they will let you get back on the snow.