3 week is a good estimate. Though it can be sooner as well depending upon the embassy, if the case is clear or time of the year.
If you applied on line, you might receive a passport request which can be any time with in a month after medicals. Usually 10 or so more days latter you would get visa. Both of these things combined might take less time. It all depends.
Obviously if you applied on paper, your passport already lies with them.
Lastly, this is all assuming every thing went well. It is possible that they have some concerns regarding your medical report, and respond back asking for further examination. I have been through with this and the cycle consumed a few more MONTHS till finally getting a visa.
So keep all possibilities in mind