I'm a US citizen currently living in Canada on a study permit. I've been flying back to the US fairly frequently for a variety of reasons, mostly for short trips (a week or so). Is there any limit on how often I can travel back and forth? I've heard of some people being questioned at the border about frequent trips back and forth.
Frequent trips are a red flag for visitors, who sometimes try to use them as a means of spending more time in a country than they are allowed under the country's immigration law. That obviously does not apply to you, because you are not a visitor in Canada and your stay in the US is not limited.
Frequent trips may also be seen as a red flag suggesting potential criminal activity, especially if there is no good reason for the frequent trips. You have a good reason for the frequent trips, and if you are not engaged on criminal activity then an investigation at the border should not have any effect other than to delay you for a few minutes.