Dear abx,
please have some patience, if ABH in Germany has confirmed that they have given the green signal to the
German Consulate in Karachi than it is clear that sooner or later you will get a call or email from them. If you keep calling them, they might get annoyed and then you wont be able to fly before May.

On the other hand please let me know in which city/town of Germany your spouse lives? Although nowadays everything is done online, but some visa officers in German consulates still prefer to have a written confirmation by post as well. This is how the German bureaucracy works;
- ABH in local town/city sends the documents by post to the Foreign Office (Auswärtigesamt) in Berlin. (2-3 days)
- Foreign office sends every fortnight, alot of documents, passports etc to the German Consulate in Karachi. (15-20 days)
So i will suggest to wait for another two weeks and dont buy your ticket before the German Consulate ask you to show the ticket.
I hope this information was useful.
Best regards.
Raj++