the three weeks at 70 we recommend is just a rule of thumb, And factors like temp during storage, and gravity of beer factor into it.
I have a detailed blog about carbonation and conditioning here.
Revvy's Blog, Of patience and bottle conditioning.
Your issue is like 99% of them...it really is a matter of patience.
I have had stouts and porters take 6-8 weeks to carb, and had a 1.090 belgian strong not carbonate
for 3 months.
When in doubt, wait it out.
