The short answer is that if you had a professional treatment and it has been three weeks since the end of the treatment with no signs of continuing infestation (i.e., bites, live bugs, new fecal matter, or cast skins), your bed bug infestation is likely to be controlled. The problem is that the true answer may be more complicated than this because of a number of complicating factors such as:
The original infestation’s size
The treatment’s method and its thoroughness
The type of house