None of the above...
The third option is
patience
It doesn't matter that your beer spent 2 months in your fermentation vessel. I bottled a chocolate mole porter after
5.5 months in PRIMARY. And it carbed up fine...in time.
The
3 weeks at 70 degrees, that we recommend is the
minimum time it takes for average gravity beers to carbonate and condition. Higher grav beers take longer. Lower temperatures take longer.
Stouts and porters have taken me between 6 and 8 weeks to carb up..
I have a 1.090 Belgian strong that took three months to carb up.
Temp and gravity are the two factors that contribute to the time it takes to carb beer. But if a beer's not ready yet, or seems low carbed, and you added the right amount of sugar to it, then it's not stalled,
it's just not time yet.
Everything you need to know about carbing and conditioning, can be found here
Of Patience and Bottle Conditioning. With emphasis on the word,
"patience." 
Read the above blog, and come back to the beer in a couple more weeks.
If a beer isn't carbed by "x number of weeks" you just have to give them ore time. If you added your sugar, then the beer will carb up eventually, it's really a foolroof process. All beers will carb up eventually. A lot of new brewers think they have to "troubleshoot" a bottling issue, when there really is none, the beer knows how to carb itself. In fact if you run beersmiths carbing calculator, some lower grav beers don't even require additional sugar to reach their minimum level of carbonation. Just time.
If you add carb tabs, you will get bottle bombs. If you add yeast it will STILL need a couple weeks to carb and then CLEAR your beer so it doesn't taste like the yeast you added.
Patience is all you need to fix this....
